Some of them include .tk, .ml, .cf etc. Would you use one? Well, paying domain renewals could be expensive if you have a lot of websites and this is a break from that.
I think having extentions is mostly a vanity thing. For instance, I have a .club cause I like the "cool look". Nonetheless, nothing wrong with that, unless you're rubbing it in to people with a sub-domain or a free extension who are more into the material not the title, lol.