Are all plugins created equal?

I see a lot of advice on minimizing the number of plugins for a site… but are some more bandwidth intensive than others?

For example, I use Page Management Dropdown a lot, which lists the pages in a flyout menu in the back end. Does using a plugin like this (that doesn’t affect the front end of the site) count, when you’re trying to keep plugin use low?

Or a plugin like BackupBuddy, which automatically backs up the site… does using that affect how the front end deals with plugins?

Thanks in advance.