A good seal will keep out unwanted intruders
Rodents love to get into the insulation behind the skirting, where they dig tunnels, make caves, gnaw on wires & plumbing, invite guests, have babies, poop and pee, then die and rot, making your hot tub stink to high heavens.
Many hot tub brands will boast about having a sealed base, but a sealed base doesn’t always keep critters out, for several reasons:
Someone’s poor attempt to keep out rats. Note the floor has a sealed base which does nothing to stop rats from entering.
So, don’t assume that a “sealed base’ means you won’t have problems, and nor should you assume that a non-sealed floor means trouble.