The benefits more than outweigh the drawbacks.
For example, AR15s are regulated. You can only buy one at a time (well, I suppose you could get 2 but then you can't buy any regulated stuff for 60 days)
I am able to get 5 AR-15 lowers, pay the $10 Maryland State police fee once, and get a break for ordering multiple lowers.
There are a few other benefits, but the main thing is not having the "1-regulated gun every 30 days" law.