If they are broken, why not? You can't use them to transport goods safely and they contain nails so people will hesitate to put them in a wood burner.

Near me (East of England) there seems to be no end of offers of free pallets from building and manufacturing trades - posts on local groups or adverts for as many pallets as you can take away. I was tempted to get some for a project, but the time to break them down put me off.