Incline is definitely a much better exercise for development then the flat press. However, when it comes to pushing heavier weight, the flat is anatomically easier to perform. The incline is the hardest, and takes a much harder toll on the upper body. Most people don't do it correctly, they lift the butt, flatten the back, and in essence make it a flat bench move.
The decline press, is by far the easiest, and leaves you the most capable of moving the heaviest weight.
Mister B is right though when it comes to the usefulness ... There's only one real benefit out of performing the flat barbell bench..... And that's just to say " I can bench X"