I think this is a good question for here but I'm not 100% sure. Please flag if it's too vague.
I've worked on many websites where common framework classes are overridden.
Since I work mostly in .net these days examples would include Page, Masterpage, UserControl, DbContext ect. I believe this could apply to any language though.
Sometimes I can see why it's done, I overrode entity framework's DbContext to include some logging code.
Allot of the time though I don't see why these base classes were created. Because I've inherited most of the sites I can't really ask why.
My question: Is it a good idea/practice when creating a new site to Override the common framework classes mentioned above? Would doing so be considered more of an old style?