You must be very careful what you say on this forum. Uninformed readers will repeat the word vacuum as a truth learned on this forum. The bath fan will not create anything close to a vacuum.
It does create a slight suction in operation. Take a square of toilet paper and see if the operating fan will hold it to its grill. That is sufficient to indicate the fan is operating satisfactorily.
In terms of effective air and moisture movement in the bathing space that depends on multiple factors including but not limited to placement of the fan. It is also beyond the scope of a home inspection. It needn’t be commented on.
Okay! I will amend my statement by clarifying that the bathroom exhaust ventilator does not create “an absolute vacuum”…! But the whole science thing indicates that at any time in the process of moving air from a higher to a lower pressure a vacuum is created momentarily (a vacuum differential) that if integrated continuously between the admission chamber all the way to the discharge point, a relatively vacuum will prevail. Thereof the popular name of the well known household device “vacuum cleaner”.
I hope this clarification serves the purpose to any down-to-earth home inspector and of course all ‘respectable house keepers’ in this blog.
The correct term is “pressure differential” - just saying. Closing the bathroom/washroom door while the fan is running, and there can be a 5 to 10 pascal pressure differential between the bathroom and the rest of the house.
Of course, this is also why atmosphere vented water heaters are not allowed inside the bathroom or an attached closet. That’s enough negative pressure to backdraft the water heater flue, which will be operating when taking a shower.
What the hell did we all do before the Fart Fan was invented? I know I grew up in at least 2 houses that had no ventilating (windows, fans etc.) and never had any issues. Same could be said for computers, cell phones…blah, blah…
I remember decades ago when Red Roof Inn started addressing the bath fan exhaust issue. The first “solution” implemented was to install a charcoal filter internal bath recirculation fan which ‘filtered’ the farts. It didn’t take long for them to realize that the bath fan exhaust needed to go to the exterior.
I have a condominium complex or several nearby that were built in the early 70’s. They all have recirculation fans with filters. A few of the units actually have exhaust fans but most only circulate the air.
when you had to go 
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