There are many reasons to collect seals: because of historical interest, because they were made by famous artists or were owned by famous people, because of the seal designs, because of the carving on the stone, and simply because of the beauty of the stone. Seals can be made from a wide variety of materials and can be very beautiful. They can also be incredibly expensive. A good piece of chicken-blood stone, for instance, can cost just as much as buying a house. It can be extremely difficult to tell one variety of stone from another and fakes abound, so unless you have a stone with an unimpeachable provenance (and even these can be forged), I don’t recommend collecting stones as an investment. If you collect because of the beauty of the stone and it brings you pleasure, then nothing else matters.