This is a very interesting question. Of course, if I do something with my spare time, then I don't have spare time anymore
What spare time means is "time for my own activities outside of work". There is never enough of this. There is always something I could do if I didn't have to work...I would play more golf and ski more. I would have more time to read, watch movies, and of course search for porn and watch porn
I have many movies on my computer that I have downloaded but can't find time to watch.
The more things one is interested in, the more work gets in the way of spare time.
There are two kinds of people who don't complain about the lack of spare time: those who love their work above everything else, and those who have few personal interests.