“These conventions didn’t just come out of thin air: they all started life as somebody’s bright idea. If an idea works well enough, other sites imitate it and eventually enough people have seen it in enough places that it needs no explanation.
When applied well, Web conventions make life easier for users because they don’t have to constantly figure out what things are and how they’re supposed to work as they go from site to site.
One problem with conventions, though: Designers are often reluctant to take advantage of them.
Faced with the prospect of following a convention, there’s a great temptation for Designers to try reinventing the wheel instead, largely because they feel (not incorrectly) that they’ve been hired to do something new and different, not the same old thing. Not to mention the fact that praise from peers, awards, and high profile job offers are rarely based on criteria like “best use of conventions.””