You have to have the chain tight enough that it won't fall off, because if it does, it can lead to a catastrophic crash and expensive repairs. The idea is to make sure it is tight but not binding.
To check the chain for minimum tightness, stand on one side of bike, reach over the bike, grab seat tube or down tube near the BB with one hand, raise the bike so it is horizontal and use yout other hand to turn the cranks. If the chain stays on, you are ok.
Il faut de l'audace, encore de l'audace, toujours de l'audace
1980 3Rensho-- 1975 Raleigh Sprite 3spd
1990s Raleigh M20 MTB--2007 Windsor Hour (track)
1988 Ducati 750 F1