I was at a job were I figured this out. Management was a mess, scope was so fluid to be essentially non-existent, and it was always the devs fault. So I said "screw it", I work 40 hours and collect a pay check, and that will be the extent of this relationship.
Sure enough, about 8 months later I am let go out of the blue for "lack of productivity" and "failing to be a team player". The example cited? When we were asked to stay after hours to help the company move offices.
Unless its your company, the relationship should always be about the money. I am giving a skill for X amount of time. In return I an receiving $Y. Anything more or anything less either needs to be put in writing, or is effectively an unnecessary gift. Perhaps it may be one you want to give, but ultimately unnecessary. And anytime the company asks for more X without giving more Y, they are taking advantage of you.