The advice is right, but I'd add this: the reasoning behind not allowing the slab to bond to the poles or collars is because the slab WILL move over time, and the poles, if set properly, will not move. If you have freezing weather, frost may move the slab up and down seasonally. My slab inside my shed moved about an inch up this winter (and went back down this Spring), an extreme case due to very cold weather here in MN. Even without frost, the slab will probably settle slightly over time if placed on fill and packed sand. It happens. If the moving part and the stationary parts are kept from bonding together, both will survive without damage. The slab would crack of held by the poles.
On the subject of collars around the poles, after reading a couple books and listening to some of the best advice on this TBN and other sources, my method was this: Drill hole, tamp bottom dirt flat with 4 inch diameter wooden fence post, then add three or four shovels full of crushed rock (or sand), retamp with fence post, drill a 1/4" hole into each surface of the pole, about a foot up from the bottom end, drive a landscape spike (about 10 inches long, maybe 5/16" diameter) into the holes so maybe three inches of the spike is in the wood and most of it is sticking out, drop the pole in the hole, locate and brace for plumb, now pour in the concrete collar, concrete will bond to the pole and especially to the landscape spikes. I use about half the hole depth for concrete. The bottom of the pole can drain since it is setting on compacted crushed stone or sand. The concrete collar adds a lot of bearing area and makes withdrawl much more difficult. After concrete cures a day or so, I backfill the hole with more crushed stone, and a layer of dirt on top.
