By tactical destruction, I mean being able to blow holes in walls, floors, ceilings etc., and using it as a gameplay element to help you flank, escape or hide more easily.
For example: You know that someone is on the floor below, under you. You want to get down there to kill them, but you can't make it in time with the stairs. So you pull out your C4, grenade launcher or whatever and shoot the floor, blowing a hole in it. You jump through the hole and knife them.
Or another example: Someone camping and shooting your team through a window, and they hide too quickly for you to pwn them. So, you pull out a grenade launcher and shoot the window, which makes the window a lot bigger. Boom, no more camper.
So, here is why I think it should be implemented:
It adds unpredictability and dynamics to the environment. You won't ALWAYS be able to go up into that tower to snipe, because someone might have blown it up with C4. Is there a map that is full of campers that hide out in 1 building? Shoot up their base, destroy their cover.
See what I'm getting at? With destruction of this sort, the map will not always play the same way every time. You may have heard something of this sort in BC2 reviews, but it makes the maps feel less like game arenas and more like dynamically changing battlefields. You can use the environment any way you like, to help your team or to remove enemy cover.
Another thing it adds to is the speed of the game. It keeps everyone constantly alert and moving.
Bad Company 2 is a great game (IMO, I play it on my PC). But, I think that with Crysis 2 graphics and the Nanosuit 2 AND tactical destruction, it would be even more awesome. One thing about BC2 is that the physics aren't really that great.
Crysis 2 has procedural destruction. Combine that with the ability to blow up the wall completely, and you've got BC2 destruction with physics and fragments.
If Crytek does it right, which I'm sure that they can, then it would make for even higher review scores. It would also really help to move it away from the 'generic shooter' path that Crysis 2 has been going down lately. I know that they try to justify it with the Nanosuit 2, but that really doesn't make up for the kill streak rewards that seem so similar to Call of Duty.
I know that shooters need to have some things in common, but Crysis 2 just somehow rings 'generic' to me. Things like bullet drop and tactical destruction would be very good for uniqueness.
There are probably more reasons I can't think of. I will update it if I think of something. As a last comment, it's just really cool to blow things up!