It depends on you really.
If you don't mind a few scratches then just use it as it is. I think stuff like invisible shields are so popular with Apple users because most of us are pretty in love with the clean design and pretty anal about trying to keep it looking as good as possible.
It's a trade off really. By adding the shield you can be sure that barring any dent-inducing drops, the computer underneath is going to stay pretty much pristine as long as you use it. On the other hand I think most people would agree that they look better without the glossy shield coating, and you trade the pleasant aluminium feel of it for a plasticy one.
I've got one on, and I'm glad I do, but I've taken the internal bit off so I can enjoy the metally texture.