The firs thing that comes to mind when knowing what Assist Mode does reminds me of Mario Kart 8 Deluxe, which is already mentioned. One thing I found out about Mario Kart 8 is that it feels like if you made a mistake in timing turns, it's rather time-consuming to get back on track. Not that I have trouble with Mario Kart 8, but I feel that this is great if I got, say, someone who might not be used to the driving system in Mario Kart 8. I am not sure how easy Mario + Rabbids becomes if Easy mode is activated, but I imagine that it makes the (I heard it's difficult) game more accessible.
Therefore, for Super Mario Odyssey, while I would likely not use this due to my overall experience with Mario games, I think that, because of Mario's popularity, getting as many people as possible to enjoy the creativity of Mario games is a great thing as a whole. There are some people who likes to be challenged like me (for the most part), but there are some who wants to be able to play this game without worrying about all of that.
I do wonder, if an equivalent of an Assist Mode would be ideal if the developers want to remake older Mario games like the Super Mario games for the NES or SNES, but I wouldn't be opposed to that.
Thank you for reading.