I have asked tons of questions about this....learned a lot here, a lot from the pool store (I know, I know, but they are awesome), and from my neighbor. This is the model I have.
http://www.craftsman.com/shc/s/p_10155_ ... +Air+Tools
SCFM ratings that are high are used for moving mass quantities of air over a long path, such as blowing out a sprinkler system, without having to wait for the compressor pump to catch back up. This is why you see sprinkler companies with HUGE compressors on the back of their trucks. Paint guns also require a large SCFM.
I have heard of guys using pancake compressors, and some with these utility compressors, as you have listed. They are pretty much used for airing up tires, and light work, such as a brad nailer. I guess it would all depend on how your lines are laid out.
I use mine for a variety of things, so I don't have it just to blow out my pool lines. My main question was how many PSI should I be blowing through the lines without blowing them up? The main consensus was anywhere from 20-40 PSI. This is nothing for a larger compressor. Low volume air + larger tank= less pump running on the compressor.
As for the Harbor Freight deals, you might be surprised. I love the joint, trust me. It's good for generics, and things that you might use once or twice. I will usually head to Sears for power equipment, but I have been known to buy refurbished power tools from HF from time to time, and still be using them years later. If this is going to be the main purpose for compressor ownership, I say entertain the idea, especially if they are having a sale. If you plan on equipping yourself with all sorts of tools and projects that require air, I'd go to Sears, IMHO. Might quit on you the first time you use it.
I plan on using mine for closing this year, and I have no idea if it will work or not. I'm assuming it will, but I'm anticipating issues with blowing out my spa lines.....spa sits about 6 feet about pool level. That should be interesting, so we'll see what this compressor is made of.
GK