Automate everything (practical uses of Bash part 3)

Last time I provided some quick shell script time-savers. The goal of automation is saving time and providing focus on important things rather than tedious yak shaving. The time it takes to write a little script is hardly anything compared to the time it saves.
So here are some more useful tips including how to list folders by size, read and verify user input, and find files by date, loop over them and apply a command (like mv or rm) . . .