It depends on the terms and conditions. Most free spin bonuses are not 'wagering free', meaning you have to play through your bonus amount a number of times before being able to cash out. I can be tricky to arrive at this wagering limit in order to cash out real money. That said, it's worth remembering that playing slots for free can be fun and build on your game playing experience making it a worth while experience to claim the bonus even if it's tricky to walk away with a hard cash win.