Due to how Resident Evil 5 adds up IGT (In Game Time) it can be confusing to newer runners how to properly use resetting checkpoints to save time. The point of this guide isn't to clarify what is and isn't a tactical reset (there is already a guide that) but to point out the specific areas in the game that a reset can be used to directly save time. To sum up the guide quickly any reset used to fix a mistake will invalidate the run. Every checkpoint in the game can be reset, but resetting most of them is pointless, and a few of them will actually lose you time. Below is a list of all the checkpoints that will directly save time if reset.

1-1 and 1-2 do not have a reset point that will save time. 2-1 - There is a walk in checkpoint after the bridge (just down the stairs) where a truck tries killing Chris and Sheva. Resetting after this checkpoint will save a few seconds. It regroups both players at the checkpoint. 2-2 - There is a walk in checkpoint shortly after exiting the house that's just outside the caves. After climbing a rather large ladder and jumping down off to right a little ways the checkpoint will appear. Resetting after this checkpoint will save a few seconds. It regroups both players at the checkpoint. 2-3 does not have a reset point that will save time. 3-1 - There is a walk in checkpoint shortly after leaving the main swamp area. After jumping into waist deep water and running a ways steps to elevated ground will appear. Just after the top of these steps a checkpoint appears. Resetting after this checkpoint will save a few seconds. It regroups both players at the checkpoint. 3-2 - 1. In the middle of the chapter there will be an area where fire is blocking the players path. Killing either chainsaw Majini will give the player a checkpoint (This is only consistent on amateur. Other difficulty's may require both chainsaw Majini to be killed) and resetting this checkpoint will spawn both players next to where the fire was blocking the path to the exit. Note that if fire is blocking the path before the checkpoint is gotten it will still be there after the checkpoint is reset. If done right this saves 10+ seconds, 2. There is a walk in checkpoint just after the top of the elevator that Josh activates for Chris and Sheva. Getting this checkpoint and then resetting it will spawn Josh outside the elevator. The faster Josh can get to and unlock the door the better. This saves a few seconds. 3-3 does not have a reset point that will save time. 4-1 - 1. After Chris and Sheva fall through the trap door where a QTE is done to not take damage a reset can be used to save time. The recovery animation from falling will be taken away, saving a couple seconds. 2. There are three different resets towards the end of the chapter that save time. They are all right after Chris and Sheva pull one of the chains that change the layout of the stairs in area. Resetting after the 3rd chain pull will turn both players around, saving about a second. Resetting after the 4th chain pull will place both playing a little closer to the stairs, making the trip down stairs to do the split chain pull a little shorter. Saves less than a second. Resetting after the 6th chain pull will place both players 2 steps closer to the boss spawn, saving about a second. 4-2 - 1. There are two walk in checkpoints in the first area of 4-2. They are used differently from solo to co-op but resetting at either of these checkpoints will spawn the player that's farther away right next to there partner and where the checkpoint was reached. One is at the spot where Chris assists Sheva in getting across a gap to get a piece for the locked door. From here the other checkpoint is reached while running to the last door piece, right before the last dangerous sunbeam. 2. The played gets a checkpoint for every door piece put in the door. Resetting after the second door piece is put in will spawn both players at the checkpoint. This saves a lot of time. 3. At the end of the chapter there are three areas where sunbeams need to be directed in a certain way to proceed. Resetting the second area gives both players a more favorable spawn position to beat the rooms puzzle. Saves about a second. 5-1 - There is a walk in checkpoint shortly after the first real encounter with lickers. It will be right before a set of stairs and right after the 2nd spin valve and kick door. Resetting here will regroup both players and face them towards the stairs they need to run up. Saves a couple seconds. 5-2 - In the middle of the chapter after the first conveyor belt area there is a checkpoint a couple steps after a red door both players need to kick down. Resetting here spawns Sheva slightly closer to Chris. The time save is very small and may cause the first Majini to throw a grenade sooner. Might not be worth it...
6-1 - 1. There is a walk in checkpoint at the beginning of the chapter. Its just after a button is shot/ pushed (shooting it is faster) to raise a object that's in the way. Resetting at this checkpoint spawns both players together. Saves a couple seconds. 2. The very next checkpoint is also a walk in checkpoint. The checkpoint will appear shortly after climbing a ladder. Resetting here spawns both players together and saves a few seconds. 3. There is a walk in checkpoint towards the end of the chapter. The checkpoint is reached as soon as one player reaches the top of the ladder that's just before the red JJ mini boss. Resetting here spawns both players together and saves a few seconds. 4. In this same area there's a unique checkpoint that can be reset to save time. The checkpoint activates as soon as one player reaches the red keycard door after the second keycard is grabbed. The player who grabbed the first keycard can stand by the door while the other player grabs the second keycard. Resetting this correctly can save about 10 seconds. 6-2 and 6-3 do not have a reset point that saves time.

 Note that the way these resets are used to save time vary from solo to co-op, and some of them aren't possible solo. I hope this guide helps clear up any confusion about tactical resets for newer players and helps people who have been playing for a couple months save more time. GL with your runs!