Re: Advertising is often overhyped...
"lets say they spend 100m a year on advertising, do you think they would sell 100m less product if they didn't advertise?"
Conversely, let's say you don't spent anything on advertising, but decide, at one point, to spend $1m on advertising in the next FY. The only thing* that would make doing so worthwhile is an increase in sales large enough to return profits at least as large as the expenditures on advertising. Not sales -- profit. Otherwise, you're throwing money away.
An alternative to advertising: instead of the 'spend' aggravating societal noise with inane ads of all kinds in various contexts, pay your staff/employees more, tell them that you're doing so with what would otherwise be the advertising budget, and tell them why -- namely that you are hoping to encourage them to invest, in some sense, in some way, in the success of your business.
* Well, not exactly the only thing; this is shooting from the hip after all.