My daughter just bought a house. The hot tub sits directly on the deck. My father, who had a hot tub, said he believes that it should sitting on a platform/riser (because his did) that raised it and inch or so off the ground. The hot tub has been here for a while like this and I have seen pictures of others who have thier's set-up this way.
Is there any problems with this? What is the reason for having them sit on the platfrom to raise them an inch or so?

I'm not sure about a platform but I had a hottub that I sat directly on the deck and it eventually came through my deck we never ever used it so it never had water in it and it would way more heavy if there was so I would say directly on the deck is a bad bad bad idea

How high off the ground are we talking? If you have space, set a couple of 4X4 under the tub and

Your can set your tub directly on the deck if it was built to handle the weight of the tub, 300 gallons of water and 6 people. Most decks are not built to this level of structural strength. Until we know more about the deck design I'd says its an accident waiting to happen. Most tubs filled with water and people weight oover 1.5 tons. Spread that weight along the perimeter of a tub and you have several hundred lbs per square inch not all sitting on a jist. Or post.

My daughter just bought a house. The hot tub sits directly on the deck. My father, who had a hot tub, said he believes that it should sitting on a platform/riser (because his did) that raised it and inch or so off the ground. The hot tub has been here for a while like this and I have seen pictures of others who have thier's set-up this way.
Is there any problems with this? What is the reason for having them sit on the platfrom to raise them an inch or so?

Maybe not worded correctly above - the deck structure is not in question. The deck is built to handle the weight. The hot tub has been inplace for a few years.
My question is, my dad's hot tub had a riser/frame/platform (for lack of better description) about 2 or three inches high that the hot tub sat on. This hot tub doesn't have, but sits on the deck instead of on this platform. I think the only purpose of the riser/frame/platform was so that the side panels could be easily removed from the hot tub(having that gap between the deck and the bottom of the pannel. So I am trying to find out if there is a true need for this platform like my dad had on his - or is it just for the reason I stated above.

There's no need for a platform.