If you think you'd like/need to set up a lot of songs and/or setlists, and maybe have a need to clear and set them a lot, then it can save you a whole heck of a lot of time. If you just want to reprogram a couple of IA switches and/or bank assignments over time, occasionally changing an IA switch or two as the whim strikes... then it may not be necessary.
Setting up, naming, and managing songs I've never done personally, but I could see that being very exhausting from the front of the unit itself. I find switching out the occasional IA on the unit itself can take like 5-10 seconds -- even if you're even only half used to the menus -- so firing up MFC Edit for that might take more time really. Though if you're the type who absolutely hates paging through parameters hunched over a unit and wants a quick and easy way to set similar stuff all at once from the computer, it's worth every cent of the small $30 price tag.
All that being said, it's def one of those: "ymmv, everyone's needs are different, value is in the eyes of the beholder, etc" sorta things.