I feel like it depends on a few things.
1. Do you have 100k subs and make a living off of your YT channel? Ads are a given. If you have that many subs, you probably put a TON of time into your stuff.
2. Do you have a very small channel and trying to get more subs/viewers? You're at the bottom of the heap and trying to move up. No point in annoying people with ads.
3. My own situation, we just topped 700 subs in the last few days. I don't think that's really anything but, we put around 60 to 90 hours into EACH episode of our web series. So what I do is put all the ads on it except for the non-skippable ads at the beginning. I don't use those anywhere on my channel.
So for us, two out of the four of us are doing this full time and fully intend to make something career wise out of film. We're starting our own advertising campaign outside of YT and submitting stuff to people that are connected in the film/tv industry. I feel like we should acclimate viewers to the small ads right now.