I've booked 1 past and 1 upcoming cruise (both 3-nights on the Wish) less than 30 days in advance. The only downside for me was not being able to check-in 35 days (Gold) in advance, therefore getting later Port Arrival Times (12:30 for my last cruise, 1:15 for my upcoming cruise). What I did realize on my last cruise is that having a later PAT meant that the cruise terminal wasn't crowded, and the boarding process was actually more efficient. With my upcoming cruise, I'm actually thinking the 1:15 PAT could work out to my advantage because rooms are ready at 1:30, so we should be able to go straight to our room to drop our bags.
I always choose late dining which is typically the least popular, so that has never been an issue for me.
I also rarely book excursions through Disney (usually use an outside vendor).
As for activities, it often requires persistently checking the app for availability, but I've been able to book a lot of popular activities within the 30 day window. For my past last-minute cruise, I was able to score both Palo Brunch and a Serenity Bay Cabana. For my upcoming cruise (which we booked 27 days in advance), we have booked Prima Notte at Palo Steakhouse, a Martini Tasting, and dinner at Enchante. I'm lucky because it's my sister's hobby to continuously check the app for availability - you'd be surprised how many things open up in the week before the cruise!
Now, the biggest PRO to booking a cruise last-minute.... less time doing the countdown dance! We're leaving on the Wish next week, and I'm so excited!