Is insulating a garden house sensible or unnecessary?

Why do you want to seal the joints between the slabs? The water seeps away there anyway? I am planning a slab foundation with curb stones for my house. I wanted to set the curb stones so that the exterior walls just remain in the area of the slabs. An insulated floor probably won't bring anything in the metal garden house. The walls don't insulate at all.

I don’t want to seal the joints of the panels in general, but only the minimal area where exactly the contact surface of the side walls is. This is intended to ensure that no water enters the house at these points (rain, etc.). However, this is not the issue here anyway.

Of course, the side walls are not insulated, but that is also part of my question. Does it make sense to insulate the floor (and possibly the roof) or not? The roof is only to be considered additionally in this question because it can easily be done later... The floor, however, is as it is, I can’t insulate it afterwards. Since I simply lack the expertise for this, I wanted to ask here... maybe experts say it’s unnecessary, or they throw their hands up and definitely say to insulate if you are doing it new anyway. If it were already standing, it would be as it is, but since everything is still in the planning stage, I could react :)

Addition: Regarding the infiltration capacity between the slabs: I anyway wonder how that is supposed to work inside the house, because a vapor barrier foil must/should be laid between the gravel bed and the slabs to prevent rising moisture. But that means on the contrary, nothing can infiltrate there either!? Well, not too much water should occur inside the house that could/must infiltrate..... unless you clean the floor with a water hose or something :D

Insulating the floor and roof is completely wasted money as long as the walls insulate zero, nada, niente. And as already mentioned, temperature is only part of the mold problem. The issue in living spaces is that you have warm (and therefore more humid) air in the room, but in old buildings the walls are cold. This causes moisture to condense in poorly ventilated corners and mold forms. In the garden house, however, you normally don’t have warm air in the room near the wall. I am a bit confused about your floor. On the website, the pictures all show ridged metal sheets. So no water comes under the house from the inside anyway? And from the outside it is only a problem in places where moisture could stay longer, that is where the wall touches the slab. But at the joint the water runs right down and the wall in the air dries out?

May I ask what exactly you mean by proper construction?

I mean to avoid water entering anywhere due to construction errors, ensuring the roof is watertight and ground-contacting parts do not absorb moisture. I do not know the house, but your idea to separate the (wooden) side parts from the stone with a foil is already going in that direction.

I am a bit confused about your floor. On the website, all the pictures show tread plate. Then no water comes under the house from the inside anyway? And from the outside, it is only a problem in places where moisture could remain longer, that is, where the wall touches the slab. But at the joint the water runs straight down and the wall dries in the air, right?

You probably meant that because of the tread plate no water comes into the house from below, right? The manufacturer’s pictures always show the tread plate, but that is an accessory... it costs a hefty 350-400€ for our 4-5 sqm hut. I don’t particularly like this tread plate anyway... I also imagine it as "rattling"/noisy. But it’s not completely sealed, is it? Moisture also comes in through the gaps between the individual metal plates, doesn’t it? Admittedly, there aren’t many... probably 2-4. That’s why I wanted to rather use paving slabs for the floor, which would at the same time also be the floor inside the house. But I am still not so decided about the foundation and the floor...