Tightening toilet bolts is a fickle business. Whether you are working on the tank-to-bowl connection or bowl-to-floor connection, there is that fine line to want to creep up to but not pass.
Toilets are made of vitreous china and if you put too much stress on them they can crack.
So the question of how tight do you tighten bolts becomes how good is good enough. If you continue to tighten toilet bolts, the toilet will crack, so you have to know when to stop. The only problem is that usually only comes with experience.
I would first suggest using a very small wrench. This will make it so you are cognizant of the pressure you are placing on the bolt and nut. If you use a large wrench, you gain leverage on your side and in my opinion are more likely to crack the toilet. So use a small wrench and take incremental turns on it. Tighten it slightly and check for movement of the bowl or tank, whichever you are working on. Also, alternate tightening the opposing sides of the piece you are working on. Whether or not it is a bowl or tank, tighten one side slightly and then the other slightly then test for movement. If you hear a “crack” you will be buying a new piece.