With a fully-floating Floyd you get:

• smoother vibrato
• another way to increase pitch, even on open strings
• pitch increases greater than you could ever bend
• flutter

A decked Floyd (like EVH used) is more restrictive. Sure you get tuning stability (by that I don't mean generally, because fully-floating trems have great tuning stability, but I mean for changing tunings or when you bend other strings) but that's a trade-off that not everyone wants to make. When you can do more "tricks" with your bridge, you can be more expressive. The question for anyone is do they need the extra vocabulary to say what they feel, or is it worth the drawbacks.