Does it help to snip suckers and extra leaves off tomato plants and does this work for bellpeppers and grapes?

I certainly helps to nip suckers off your tomatoes Lovegreen. It keeps more energy in the main plant and results in bigger fruit. I usually only remove leaves that are blocking light from the developing fruit.

Not sure about the same applying to grapes but it does apply to bell peppers. I prune off all suckers or side shoots from my peppers. Bigger and better fruit is the result. Also you get stronger plants which can support the fruit more effectively.

Definitely remove the long tendrils on the grape vine that have no grapes on them and any leaves that are covering bunches of grapes. Wine makers prune their vines very hard each year to encourage the growth of just a few choice bunches of grapes. If there are lots of small bunches of grapes thin these out too to encourage good growth in the remaining ones. Our vine produced good table grapes every year until we had to move the greenhouse and could not move the vine - lord knows how old it was!