https://www.irs.gov/uac/Business-or-...for-Deductions
This is pretty much it in a nutshell; the IRS doesn't want you declaring a risky unlikely-to-ever-show-a-profit hobby (like snake breeding) as a business so that expenses can offset earned income and lower your income tax bill for years and years.
Most people are much better off running as a hobby, not worrying about maintaining separate business accounts and/or a business structure like an LLC or Corp, collecting and remitting sales taxes, checking local zoning ordinances and HOA regulations to see if a business license can even be issued for your home address, etc.