You have business ID to sign up for business services, should you choose to sign up for any of them.
With some company structures (examples: corporation, LLC), your personal assets can be protected from any legal actions brought against your company.
And registering your company as a legal entity, and paying taxes on your income, keeps you from having to pay penalties later down the line. The government may estimate what you would have been earning, based on your industry - and if you're a small hosting company, do you really want your income estimated as being equal to, say HostGator? Especially if that's the figure the govt. uses to come up with your back taxes and penalties?