The converse is that if you have many unused variables some of them are used in some contexts but not others and then when you use FIND to find occurrences of a variable you will find many which are not relevant and some which are.

Overall the code gets smaller and easier to understand when it only has things that need to be there. If you comment out a an unused variable you can see from find-results that in effect that occurrence cannot matter.

Unused variables are "noise" that hide actually important things.