I automated my backupping, for example (yes, I wrote my own script for that. Shame one me.).

When thinking about writing a general script, I try to abstract my task and find the smallest and fastest possible solution (hint: don't spawn
too many processes) and then I write it down.

Most of my commands are just saved in my command line history, and my shell (fish) has a really good
searching function and autosuggest what makes me easily find whatever I want.

I don't really have any scripts running constantly in the background, but the scripts I wrote can be found at
https://github.com/pranomostro/script

I use shell functions for aliasing stuff, everything more complex than adding a default flag or
wrapping with rlwrap deserves an own script.

For building, I use make (it's everywhere) and also shell scripts.