There are drill bits on the market that are designed to be used in an impact driver. The advantages of using these instead of conventional drill bits in a combi are that they give you one handed drilling (they don't try to whip you round when they come up against torque like a combi would) and they are quite a short power tool so they'll get you in places where your combi won't.
Just don't make the assumption that anything with a 1/4" quick change hex shank will work in impact drivers. Not all of them are impact driver rated. They're not all able to withstand the higher torques that these power tools can kick out. The 1/4" quick change shank is very popular in the USA and they have combi drills that will use this bit holding mechanism rather than a 3 jaw chuck. This means that there are loads of accessories produced with these shanks but they're not all impact driver rated.
The downside of impact drivers are the noise but once you've used one, you can put up with that.
I have a 3 speed impact driver and on it's slowest speed will give you very precise control. Useful for delicate operations like fastening pattress boxes.
The best way to buy would be to wait for a tool show at your local wholesaler or an exhibition like Toolfair where you can pick up a twin pack (combi, impact driver, two batteries and charger) for decent money.