He comes off as a bit of a scumbag on the show - he frequently makes exploding offers that will expire if the entrepreneur doesn't accept them within 30 seconds, or he'll state that he'll withdraw his offer completely if they even talk to another one of the "sharks" about the possibility of another offer.
After watching the show I'd be very wary of working with someone who negotiates with people like that unless there was a more equal footing.
But the reality is that most people who go on the show need sales, and having Mark Cuban willing to advertise for you on Twitter and such is very valuable for a growing business. His "expertise" is of little to no value. I certainly agree with you there.