I'm self-employed, which means I can arrange my time however I want, therefore I can hit the gym every day in a week. I also do have the energy to do so.

But, I've heard it's not a good idea. Why so? How many days in a week should I work out? How should I arrange these days? (go, go, go, go, rest, rest, go), or (go, rest, go, rest, go, rest, go) ?

EDIT: I'm talking about lifting weights in a gym in order to gain weight, strength and muscle. I'm relatively low-weight, I don't need to lose any weight.