Davy Brion has a good post about overtime that is worth a read.
I’d like to expand on my comment to his post.
I should note that this applies beyond IT.
It seems to be an expectation in many organizations that the people who work for them should need to work more than 40 hours a week. This is unfortunate, but it is what it is.
As a contractor, you can bill for it. End of story. If the organization you work for, for whatever reason, good or bad, has this sort of expectation, then your billing invoice raises this as an issue for them. They can choose to accept it, modify your expected hours, or get rid of you, all of which are valid choices for them to choose, but it raises the issue to management.
Another advantage (which generally trumps the billing thing) is very clear: you don’t have to care about certain types of office politics.
In the times that I have been an employee (and sure, this reflects on me, that’s fine), it has mattered if Employee A who does less work and provides less value than me gets paid more or gets other benefits (whether specific like salary and options or more vague like time off, being able to work from home, etc.). Even when I knew the specific reasons why this occurred (for instance, I once had to work for someone who was clearly less qualified than I was because that person had to be offered a particular position in the org chart to come back to the organization…it was an understandable business decision), it was highly annoying to know I should have been at his position or even above it based on job qualifications.
When you are a contractor, this doesn’t matter. Employee A has more pull with the big boss, regardless of skill, because of past experience? Okay. I’m a contractor. Unless it massively affects my daily work processes, then that’s fine, let Employee A do whatever role he’s assigned to do.
For all sorts of legal reasons, there are potential differences between how employees and contractors are treated, and you should be aware of them. But once you are freed from worrying about where you sit in an org chart, you are really freed from all sorts of considerations that might otherwise be relevant.