Nulling before Overwriting?

Is it necessary to clear a variable before overwiting it? For example I usually make a unit group but I sometimes overwrite this variable in the same trigger. Is there no effect or do I have to start nulling them Thanks!

The only place in which you arguably need to null something is before a function ends.

You don't need to null them, you just need to destroy the group.

thanks

another question - Is it okay for me to leave variables uncleared if i plan to overwrite them in other triggers. (GUI) What is the effect on memory if I do this?

the triggers activate very often and keeps reusing the variables

Yes reusing variables is very good, no need for nulling than.
Just don't forget to clean leaks.

thanks. Just what I needed =D