It depends - from a purely financial point of view, it is worth it for me (ie the cost of buying an extra day's leave is cheaper than paying for childcare during the school holidays for 3 children. But, it doesn't affect my targets or my work (no-one does my work on the day that I'm off and I still have to hit my monthly / annual targets for generating fees etc) so I have to make up 8 hours of work for each additional day that I take iyswim.