I've never heard anyone use this. We would say "thank you in advance for your help" but still not in a conversation. More likely, you will see it in a written request where you are asking someone for something, and, for whatever reason, you have confidence they will help you. I've used it at work when seeking recommendations or feedback, emailing the help desk, or times where it is someone's job to fulfill my request but I still appreciate them helping me. In a conversation, I would just say "thank you."

I haven’t really heard this as much as “Thanks in advance for your help,” but it basically is just thanking someone for helping you before they have actually done what would help you. For example, if someone is providing you with a recommendation for a job you could use this before you have actually helped them or you could just say “Thank you” or “thanks.”