I have 2 pairs of glassess one pair is for reading, watching telly etc and the other pair are for distance but when and why do I have to wear them?

I think you have already answered your own question here.

Driving, going to movies, theatrical events, sporting events, etc. Any place where they improve your vision of the surroundings.

Reading glasses are to see what is within arms reach or less, the other pair is for the rest of the time.