Monkeyman, shut up, you don't know anything. I actually worked on a 80% lower. Someone I know just happens to be a machinist so for 80 bucks I made a working AR-15 lower reciever in about an hour. The reasons to do it are
1. You save money, a stripped lower will cost around the same, but you don't need to go through an FFL.
2. Its unregistered, the ATF says its legal to make a unregistered AR in post ban configuration (Unfortunantly you can't sell it, sorry).
3. You learn alot, some people ie monkey man lack the knowledge, know how and the opposable thumb to do such projects. If you don't know how to complete one, learning how to is fun.
4. If owning a gun makes me feel like a big man well making one makes me feel even bigger. Seriously, why not do it. Like with changing my oil, doing it myself nearly costs as much as it does having someone else do it. I change my oil and only save a miniscule amount, but I just like doing it.