A large pen tablet has an active area diagonal of about 15 inches.
Generally I advise against getting a LARGE pen tablet unless:
you already have experience using one
or are highly confident your art style will benefit from it and you are ready to deal with the ergonomic issues that come from using one.
With a medium pen tablet most people put their tablet to the right or left of their keyboard.
You can certainly try this with a large pen tablet. But what you'll discover is that it is extremely difficult to reach the more distant edges of the keyboard or tablet depending on how they're situated in front of you.
So a large pen tablet typically means you will have to have it directly in front of you. And then you place the keyboard above it. This of course means that it's more difficult to reach the keyboard.
Often if I'm not really drawing I'll in fact put the keyboard on top of the tablet.
With a large pen tablet your hand is really moving quite a distance to do some things. So for example if you are trying to reach a menu item at the very top of the screen you might be surprised how much distance you're going to have to move your pen. This can be very tiring for some people.
If the active area is too big for you, then you should keep in mind that you can always scale down the active area to any size you want. You can make the active area match a medium sized tablet for example.
If you want a large pen tablet, pick from one of these:
Wacom Intuos Pro PTH-860: EXCELLENT (my notes on this tablet)
XP-Pen Deco Pro XLW GEN2 (MT1592B): VERY GOOD (my notes on this tablet)
Huion Inspiroy Giano G930L: GOOD (my notes on this tablet)
In this video I go through a lot of detail about what it's like to actually use a large pen tablet. In this case I'm specifically using a Wacom intuos pro (PTH-860). But the same general issues apply to any large pen tablet.