Do working adults even use their skills future credits? I have never heard of anyone going for these courses to upskill... Are these courses any good?

You can use the credits on online courses, such as those on Udemy!
There are also some institutes, such as NUS/Laselle/etc which offer interesting courses such as photography, videography. Can consider those if you're thinking of picking up a new hobby :)

I think some people do - though my (non-scientific/anecdotal) experience from speaking with people is that most people take just to claim the credits and often in something random they are interested in rather than an actual career reskilling