Poor execution management can make an amazing strategy (backtested) result in complete garbage. Understanding market structure and best execution practices are vital to a trading firms success, doesn't even need to be a quant fund. Also, if you're strategy involves trading a large amount of shares, then if you don't manage your order properly you can either sway markets negatively against you/ give away your trade to hft folks (they'll see you tryna buy/sell and then smoke you).
People pay alot of money for a good smart order router. If your execution guys can figure that out in-house, you can both save a lot as well as have more control over your order flow. I'd read about ITG and their trading algorithms for a better sense of what's going on in the execution space.
As for front office/back office, I don't really know - if you bring value to the firm (and if they are a good firm) you will get $$$.