Why do designers change the class names?

[harmor19]

I want to ask all the designers that change the class names why they feel the need to change the class names?
I copy template modifications from one template to another and I find it irritating I have to change the class name.

[SmashinYoungMan]

I add a variety of custom classes, depending on what I'm trying to accomplish. For instance, modifying the category strips on the forumhome page only. Sometimes, I make changes to those that I don't want reflected in the standard tcat class sitewide, so I'll create a new class called ".fh_tcat" or whatever.