Console Commands adds a number of useful commands to SMAPI (like to change the date, clear a map, etc). You can type
help in the SMAPI console to get a list of them. It also gives you access to the game's debug commands, which are
documented here.
SaveBackup makes a daily backup of your save files in the save-backups folder inside
your main game folder. It keeps ten backups in case something goes wrong. They are both very passive and don't do anything that would affect normal play, plus they can save you a lot of trouble when you really need them :)