Don't do it and Youtube will very likely take down your channel. Embedding external links like Spotify is in violation of Youtube Community Guidelines which states, "We also don’t allow content where the main purpose is to trick people into leaving YouTube for another site or to boost your own engagement metrics (like gaining subscribers or watchtime).
Yea it works pretty well. I dont really know this from personal experience, but I have heard others say that getting their music on youtube channels like Promoting sounds and having a spotify Link in the description is one of the biggest things that helped them grow on spotify 🙂
Any time you can put your Spotify link in front of people, I would do it. Some times it will work better then others, but its allways worth the shot!