Its always been hard to know. "about one-half the money I spend for advertising is wasted, but I have never been able to decide which half." dates back more than a century
Some spend is just in case. Some spend is for prestige (we are on TV!). Some is for vague reasons that cannot be measured.
Except for targeted online ads based on browsing/search history or other spying, most advertising is just brand/product awareness, hoping to create a memorable impression.
What really baffles me is that among people my age in the sorts of circles I interact with, that memorable impression is overwhelmingly negative. Seeing an ad at all creates an immediate negative association. "This brand/company feels they have the inviolable right to assert themselves on me and forcibly take up my attention and time". It's wild that this sentiment either hasn't percolated up to advertisers, or (more likely) they just don't care.
General, non-obtrusive and non-targeted ads don't really bother me. Maybe because I grew up with ads in newspapers, magazines, billboards, radio and TV. The latter two were most annoying because they interrupt the programming, but I understood that's how broadcasters make money so that they could operate.
Deliberately annoying pop-ups, nags, auto-playing media, distracting animation, etc. in online ads does provoke the sort of negative reaction you describe. I block as much of that as I can. I would not really mind a website that had reasonable number of static, inline ads that didn't slow down scrolling or page loads and were relevant to the content of the site. But that's pretty rare.
for me, some ads also utterly ruin the brand of the ad host.
For example: here in France we have this one company whose business model is "get a 18.xx€ refund on your order (20€/mo subscription)". its rather obvious how this kind of system makes money.
i had some elderly family members get scammed this way, and I absolutely refuse to ever return to any webside that displays this "offer from our partner". after checkout ofc.
so i get my train tickets on trainline, and amazon gets what businesses fnac and darty should have gotten. manomano must've lost a couple thousand euros of purchases from me already, hope it was worth it to them.
looking at running sneakers yesterday of a new brand I've never come across before - looked pretty interesting and bookmarked for later...within minutes of visiting the site I was seeing retargeting ads for the brand. Instant turn-off - no longer interested.
Some spend is just in case. Some spend is for prestige (we are on TV!). Some is for vague reasons that cannot be measured.