You probably will not be able to do much with a 1/4" impact driver. Valve covers yes, engine compartment maybe, but suspension forget about it.
It's a great tool but NOT a substitute for a strong 3/8" or 1/2" gun.
+1 I have a nice makita one and loved it when I was a mechanic. It's excellent for removing anything 14mm and under, IIRC it might struggle with the super tight 14mm stuff.
I tried it once on a lugnut and it did take it off, barely, but it was also under ideal circumstances, small low torqued nut, on a newer car. My top of the line 300 ft/lb 3/8" air impact was good enough to remove the lugs on 90-98% of cars, but not trucks. That's nearly 3x as much power as an impact driver and it doesn't need a power robbing adapter.
I especially loved using it for under body plastic covers, valve covers, trans pans, and spark plugs when it would reach. I would break the plugs free with my ratchet, spin them out with the impact driver, start the new ones by hand and spin them down with the impact driver, then tighten them with my ratchet. Makes the process of specifically removing and replacing the plugs themselves about 2-3x faster. What's nice too is that for automotive use, even the 1/2 sized 18v batteries last FOREVER. Just about never have to charge them and when you do it only takes 15 minutes. 30 for the big full sized batteries.
It also drives big deck screws amazingly fast and easily.