A couple examples from Linus Tech Tips when I compare the video times with all these segments skipped versus nothing skipped:
Original: 14:10 SponsorBlock: 12:38
Original: 14:11 SponsorBlock: 12:04
Original: 19:31 SponsorBlock: 17:40
I'm saving almost 2 minutes in each of these videos and there are many creators who are much worse in this regard. I've had some shorter videos where they basically are half as long once all the crap is cut out of it. It's also nice for when I don't have my hands on the keyboard/mouse such as if I've got my laptop connected to my TV. I will get some videos queued up and set my wireless keyboard down to the side and just watch. With AdBlock + SponsorBlock I don't have to touch the keyboard or mouse through multiple videos and can just enjoy things without issues. I don't have to worry about skipping past ads, sponsor segments, intros, outros, self-promo's, etc...
Overall it just makes my viewing experience so much better. At one point I had YouTube premium but it felt like I was paying so much to basically just get rid of ads but not completely get rid of them. Even with ads gone I still have sponsor segments. And if I'm having to use a tool to skip sponsor segments it starts to make me just not care to even pay for the product anymore.