It's useful knowing a little about a lot...
People say "He was a jack of all trades." and in their mind sneak in, "and a master of none." That's one of the most back handed compliments I've ever heard...
Seriously though...would you rather have a guy doing programming work for you who doesn't know anything about what you do or someone who can do the coding like a boss and understand the use? It's not a question of knowing everything about everything. It's a question of knowing enough to ask questions about the need and use.
I once saw an ad posted for a job. They wanted a computer science major with extensive knowledge of the human cardiovascular system... I think they're shit out of luck - or better be willing to pay that person half a million dollars a year...trust me that dude has a bad-ass job already... But, I could do that job... I'm not an expert in anatomy, but I know enough about it to ask the right questions to get the job done.
I have some advice for every programmer, project manager, and code monkey out there. Don't walk into a project without getting a basic understanding of the subject matter.
