Depends on the use case. I used to make websites (~10 years ago) and someone wanted an image scroller and I knew for a fact someone else would want the same thing but with a different number of images showing and maybe instead of clicking next it shows the next image it shows the next 3 images etc. We had piles of very specific scrolling scripts that weren't flexible and were hard to bring to another site. I spent a bunch of my own time making a single script that could cover most cases and it ended up saving a ton of time and became the go-to script for everyone.

Eventually someone else came in and upgraded the script and made it better before making it a core script. Now with a couple HTML classes (and a little CSS) anything can be a scroller. Options can be changed with a few data attributes.

Sometimes it's worth it sometimes it's not. I've had things so specific that I coded it like I was robbing a liquor store (get in and out as fast as possible).