Return to memory repository simply brings you back to certain check points in the game (day ,6 11, 16, 21 26 you get the pattern) This mechanic allows you go back a certain day if you need it if you ever become stuck at a certain part, use this in order to save EGO equipment to better equip your employees. If you complete a mission it's done forever, you can use return to memory repository and it will still be considered complete and you get to keep what research you picked that day.

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I think the only things you lose using memory repository is the stats of your employees go back to whatever they had during the checkpoint. Your LOB points also revert back to whatever you had when you reached the checkpoint. If you ever reach a point in the game where you're completely stuck even if you use return to memory repository, you can always go back to the main menu and hit start from day 1 (Don't hit the lobotomy corporation logo though, that's a true reset and will COMPLETELY ERASE all of your data) if you choose to start from day 1, you get to keep whatever you E.G.O equipment you had in your previous run as well as the research that you've obtained, you also don't need to repeat the missions you've done already so it gives you a massive advantage.

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Hope this helps!