Because depth is important and injuries are a part of the sport, it's really good to have guys that can fill in for a few weeks/months and not kill your team ala Ryan Goins or Mat Latos. You don't trade half a year of Joe Smith or Francisco Liriano expecting an average starter, but if you can get even a decent platoon bat or 6th/7th starter that's how you avoid your team bottoming out if one of the actual starters goes down - obviously if several of them get injured then you're f***ed anyway. At the very least a guy like Teoscar shows average starter potential and Taylor is a lottery pick, they're not just complete garbage.
The control is a bonus for one because you might be able to send them up and down as you please, and if you hit the jackpot with one of them then you have a good player on the cheap.
For the record I believe Pannone at least shows 5th starter potential.