Over the winter, I bought sseidriver97'* cordless impact wrench. Before spring comes and I get back under the hood, when do you not use an impact wrench?

From experience, it'* mainly used to loosen things. It'* also not to be used instead of a torque wrench. Anything else?

if a nut is stuck, spray with penetrating lube, then let it soak in, use the impact to loosen, but just a quick brrraaap, then reverse it and another quick bbrrraaap then loosen again bbrrraaaap etc.until it spins off easy. other than that, just common sense. nothing brittle!

Don't use it to torque lug nuts. You can put them on, but finish with a torque wrench at 100 foot pounds.

If you have a tight nut or bolt that would cause grief if it snapped, manifold fasteners, torque converter bolts or head bolts for example, use lots of easing oil and even more patience to get them loose.
An extreme case was the Triumph Stag from the 70s, if you snapped an inner head stud much higher than flush with the block you had to remove the engine from the car to deal with it.
Anything requirings specific torque or degree fastening should never see an impact wrench.

On a related note, I just bought a new foot-pound torque wrench last night. Found a great deal on Amazon that had a lot of good reviews.

Also, is it true impacts eat regular sockets? My socket set is Craftsman (i.e., lifetime warranty), so I don't see a couple destroyed sockets being a problem.

Your better off getting the impact sockets you need, like for lug nuts. No need for a whole set. I mainly use my impact for taking things apart. I either use a air wratchet or by hand to put it back together.

yeah what they said the only thing i ever used it to put together was exhaust clamps coulda used it last night lol

Get impact sockets. Because hand sockets will get stuck on the nuts/bolts when used with an impact.

Impact is for removal only. Except in a few cases like axle nuts and HB bolts. You mention you bought one, yet...in all my mind reading ability...I can't quite figure out how much torque it has or if it'* too large to fit under the hood in spots etc.