They can be handy for backups. Aside from that I seldom use them. I have a load of them kicking around.
They can also be handy if you have an operating system update that breaks the network, or some other technical glitch that makes networking impractical. And if you're wanting to transfer data onto a computer that might be compromised in some way (virus, keylogger, whatever) a device you can write-protect can be a useful thing to have.
Don't currently use any. Would need adapters to plug them into my laptop anyway. My computer backs up to the Cloud and I run a backup on an external hard drive periodically.
I do have a few laying around I need to decide whether to load onto my laptop or just keep them.