They need to be strong and stable
I think hive stands are important because they need to be strong to support an increasing weight during the summer and at a comfortable height for the beekeeper. They also need to be stable, so the hive doesn't tip over when the supers are being levered with a hive tool or when they are being removed. Many beekeepers don't seem to worry about what their hives stand on and I have seen some rather strange things being used.
When inspecting a colony you need to have enough room to put equipment down and to work without cluttering up the area with bits you can trip over. You also need to be able to easily remove supers and inspect the colony without stretching too much.
WBC hives have their own legs but I find they are still too low for me, giving me back ache, which I suspect is the same for many others too. They can be raised on concrete blocks or similar. It is usually only single walled hives that need stands.
An amateur beekeeper with only a few colonies will probably have their hives set out singly. The appliance manufacturers now supply some good stands at a reasonable price, but they may need raising to a height that will allow you to inspect the colony comfortably. A reasonable carpenter will be able to make their own hive stands and this is a good way of using recycled wood. A wood preservative should prevent premature rotting and making sure they are not permanently damp will increase their life considerably.
Concrete paving slabs are the right size for single hives and will aid stability. They are often available free and a keen eye will soon find them. The good thing about them is you can often see what is going on inside a hive by what drops out of it.
If you have more colonies in an apiary or you are short of space you can have stands that take two hives. This is what I do, but you need to be careful about the distance between them. This may depend on the material available, but the important thing is to have enough room to remove the supers. If you have enough room to place a nuc between them, you will find that useful.
I lay two standard concrete blocks on edge with a metal rod or bar driven into the ground either side to prevent the blocks tipping "windscreen wiper" fashion when pressure is put on the hives. On top of these I lay some lengths of timber about 1.5 metres long and nail a strap between them at each end. When treated with wood preservative they last many years. This is a good use of recycled wood, but other things can be used, such as scaffold poles or angle iron.
Be careful not to have things that stick out such