Pretty much what Gearhop said. There are some good unusuals that you can ONLY get through unboxing though. For example, I really want an Infernal Smoke Didgeridrongo, but there's only one in existence and it's not for sale; a lot of really nice unusuals are like this, and unless you have literal God luck, you'll just have to accept that you'll never get them. If you still want to fuck around and unbox a bunch of crates in an attempt, though, then it's entirely your choice.