I am not a UI designer by trade nor by experience, not that I would count at least. Still there have been countless projects that could have, would have, and now will benefit from advancing my experience in that realm. I jumped on it the service once and not being a member lost my code, that i've now been looking for for months.
So ease the pain fixing up or otherwise adapting/modify another project right?
I'm often in gedit or nano, but IDE's have come along way and are sometimes a necessary step up, as well its a way to persist or have a copy of that data i can quickly trade from machine to machine while I am on multiple ones, and at a glance it seems it doesnt shake hands with google when I come in and out. Why codepen in particular though? Because its elegant in design and used by countless UI folks who are really talented. Which makes it more interesting, and fun. I think I even saw Dangermouse somewhere around how cool is thaht? I can safely promise I won't be bumping into him anywhere near my Gitlab Server!
Designs here are in some cases remarkably well thought out and executed and on display, which is a bit like a great painting in your office but with the painter there alongside ready to advise on his technique I find that inspiring and just plain cool while i'm researching other types projects. The ease with which I can apply stylings to private projects as wrappers lets me basically doodle a flower around something that is not a flower, its great fun and as I kick around I will no doubt publish tidbits hopefully with growing frequency and demonstrating a growth in technical skill and or artistic mindedness. Mostly though you will see 5 versions of random shit because I compulsively save, a byproduct of serious hardware challenges of late culminating in doubling work hours which is also where Codepen is nice to use, working 100% of my waking hours, its kind of nice to just screw around or be productive or blur the lines between the two !