I do IF there appear to be any kind of litter or other
detritus visible on the carpet's surface. I don't do it just to change the swirls pattern to a vac pattern.
The purpose of postvac is to groom the carpet.take out the distortedness that op causes on the yarns due to heavy agitation,the yarns get twisted out of shape,the post vac,it has to be done while the carpet is still damp will correct this {you also do this to correct tip bloom}. You don't have to post vac all carpets, like the nylon or orpheln {spelling} type which are low looped like a commercial carpet,because there is no pile to distort.Hope this helps.
Post vacumming "residential carpets" is imperative. After OP cleaning the carpet is open to vacuuming, now things that would NEVER come out before you ran the OP over it will. Plus Op'd carpet should always be groomed with a vacuum while it is still damp.
To post vac really is the finishing touch isn't it? I do wonder just how safe it is from electrical shock. I use vacs with by-pass motors but I don't know if this helps or not. Is this really safe to do or should be all be using air turbines?
i dont know Steve, but slightly off topic to your question :
i use a Dyson for clients w/out pets and a Bissel Cleanview for those WITH pets. the Dyson with it's auto-adjusting height NEVER get's moisture in it and doesn't get "gummed" up with damp staple fibers. but the Bissel ALWAYS does. but since the Bissel has a manual hright adjustment, it is probably cause i am leaving it to low to the carpet.