I have gone to a few, it's pretty fun if you are in to looking for "valuable junk". I have always liked buying and selling from thrift stores, garage sales etc. I just don't have the time for it now.
The time I went there were about 15 units up for auction. They have a real auctioneer which is always entertaining.
Most of the units were junk - lots of old couches, mattresss, broken lamps, and other furniture. As mentinoed you can't dig around you can only peer in and try and see if there might be something good tucked away. I'd imagine it takes practice to develop some intution to know what a good unit looks like...
The last unit of the day at this place I went to was a huge unit, you could park two cars in it. All it had was a barrel that had 2 pairs of water skis and some archtiecture blue prints and two 4 foot tall boxes some paradigmn floor standing speakers. So you should be thinking OK what kind of person was paying for this giant storage unit with not much in it - a rich person - (Also, the blue prints, the skis, and the speaker boxes).
Funny thing because since you couldn't touch people were basically taking a big risk on whether there were speakers in the boxes or they were just empty boxes. People who buy high end speakers do usually keep the boxes in case they want to re-sell them or need to ship in for a repair. I was sure they were empty. I bid something like $100 and got out. The unit went for around $250.
The boxes had the speakers in them.. the retail on them was about $2000 for the set, so the person who bought that unit didn't pretty well and didn't even have that much junk to move out of it.
Yeah most people had trailers to load up all the junk on and they are often flea market dealers looking for stuff to sell. There would be some money to be made I'm sure offering to haul off junk for other people also.
I say go for it, they are fun just don't get carried away in a bidding war that's what they want you to do!
p.s. you might also look in to other auctions. A friend and I went to an auction at a community college. We were looking for mid-century furniture and stuff like that but we ended up coming home with this giant kiln. Like the kind you melt metal in. We got it for something like $20 no one wanted to haul it off. He was going to mess with it but it sat in his back yard for 2 years until his wife told him he needed to get it out of there. So I put it on ebay and sold it for something like $300. That's pretty cheap, they cost $1k's but the buyer was buying it sight unseen and having to freight it cross country.
