There is no reason not to end with a regular slip stitch. I think that’s always going to be a perfectly great way to finish off a project. I like having the invisible finish as a second option. There are just times when I choose it, like for the final round of a beanie or the cuffs on a sweater. With the invisible finish off, all your stitches blend together in a way that I find satisfying. It’s definitely a choice and not a necessity.