You would be subject to fines and (in extreme cases) imprisonment. In the long term, it reduces the incentive for creators to create, leading to less choice for users.
The best way is to use exclusively your own original work, but this is not always feasible. When using others' work, you must properly attribute it, and in most cases you will need their permission.
It depends on the nature of the business. Some create content they wish to protect, some need to license content from others, and some exist exclusively as middlemen between content owners and users.