Everyone's experience changes when a company begins to consider ad revenue.
How those changes shake out is hard to predict. It's not a stretch to suggest that even little things change for everyone though. Adding ad revenue changes how a company thinks about nearly everything, whether they're aware of it or not, and ultimately the end user suffers.
For example, Netflix would likely start trying to tweak content discovery in a way that benefits advertisers. Rather than show me content that matches my historical interests, they show me content that optimizes ad revenue as well. It's unlikely they'd maintain two different "ad-free" and "ad-full" recommendation algorithms.
Motivated by pressure from advertisers, Netflix might be less inclined to produce or provide content that made advertisers uncomfortable or benefitted an advertiser's competitors.
When producing content, they now have two bosses: subscribers, and advertisers. Both have entirely different expectations. Those expectations push Netflix into making compromises, and rarely do those compromises produce outcomes that are better than if they only focused on making one side happy.