Hi Guys
I only prevac on about 1 in 10 .
JasonL I believe only uses rotary where a pre vac is obviously important, but TM's are so powerful that in practice there is no benefit as the flushing of the water and the power of the TM will remove much more dirt than vaccing and also all the dirt that would have been removed by the prevac.
The main exception to this is dust under furniture which can be made more difficult by wetting, so I vac dry with the TM, being careful to add water on an adjacent piece of carpet to wet the dust after it enters my system.
Cheers
Doug