I have always resisted getting into a discussion, and would certainly never argue about the necessity to pre-vac, as everyone has their own opinion, often formulated over a long period of time, and these opinions are difficult to change, assuming anyone would wish to !!
In my early days I vacced everything religously, because I was taught to, but then started to have doubts.
In 20 years I have done many, many comparative tests on both domestic & commercial. I have come to the conclusion that in 90% of domestic scenarios, it makes no significant difference to the end result, or the time taken using HWE to to achieve that result.
Some situations obviously do require the use of a vac, such as Orientals, some upholstery etc: but I believe in the majority of cases it is both a waste of time & effort.
This also applies to commercial to a slightly lesser degree.
I have no doubt that many will be horrified by my apparent lack of professionalism, but as I said we all have our opinions & these are not easily changed.
Bryan