Can you enclose a heat pump outside, or will it restrict the air flow too much?

I'm building a house, and Some people have told me that you cannot put anything close to the outdoor heat pump unit because it will restrict the air flow too much, but I was watching the Do It Yourself Network on TV and they enclosed a unit with lumber on the front and lattice on each side. I don't want to do something like that and it mess up the units (we will have too) thanks.