The decision to do a postdoc can depend on your thesis. Doing a postdoc gives me a marketable, practical aspect as well. Your advisor, if you have a good relationship, is someone you can talk to about thoughts about your career, including ethical and social issues surrounding your choices. It's a two-way street. You have to make meetings, but also get to know them as a person outside the academic setting.
Advisors often invite students to dinner, have beer, etc.
Your relationship with your advisor is important and has a lot of influence on your life. I sometimes resent that and try to separate out the professional side of the relationship and not mix in a personal relationship. I feel more comfortable having only a professional relationship with my advisor and having a separate life. My first advisor was like a friend almost, and when I switched groups it was personally a problem. It's okay not to be comfortable socially with your advisor outside of Cornell.