In my opinion you need them for upholstery and you need them in lots of other situations. If you don't have one on the van I think it would be foolish.
Ive neverfelt the need for one in all the years if cleaned carpets and uphostery,

carpets dry quick now days , uphostery takes longer but if you tell them it will be out of action for a day they all fine .
I know loads of people that have them and never use them , lots of horror storys like pictures flying off the walls, soot coming down , dust every where etc .