The original poster has larger suitcases.
Taking luggage onto trains isn't always simple. If you're on the shinkansen trains, then you'll need to determine if any of your luggage is considered oversized and then book the appropriate reservations if it is. Otherwise, you'll probably be OK, though note that there isn't actually that much space for luggage. There are usually overhead racks (though sometimes they aren't available) and there's a space behind the last row of seats for the passengers sitting in those seats. Other trains have even less space. If you're traveling on trains within Tokyo, they're basically like subways and they might be very crowded.
Besides that, you have to consider whether the train stations have elevators (uncommon), escalators (more common, but not at all entrances), and just plain stairs. And sometimes, there are a lot of stairs! Pushing suitcases through the gates can be tricky, too, if they're larger than a carry on. You can usually use the manned gate in that case, but you might have to wait a short time. In any case, you won't have hands available for handling passes, drinks, etc. And then there are people who have disabilities, too.
So, why not just let a luggage service handle it?
As a bonus, the luggage is delivered directly to your hotel. So, you don't have to go right to the hotel after you get off the train, which means that you'll have more time to do other stuff!