This is a question I get frequently: Should I set up a new legal entity for each business I start.

When entrepreneurs are just starting or want to test a few ideas, they often group businesses under the same entity (or use a series LLC).

As soon as you can afford it (or if you have the money to start it correctly) you definitely want to have them each business in it's own legal entity.

This is primarily because of liability, financing and accounting reasons.

Liability
You want to maintain a proper corporate veil, distinct assets and liabilities.

Financing / M&A
Selling a company (moving assets, everything including domain, software, paypal, emails, etc.) is a mess if it is co-mingled with another business.

Accounting
Generally much easier if separate bank accounts, merchant accounts etc. This includes tax reasons but any sort of due diligence or audit will also be more difficult.

Partnership
Much easier to cut a deal with joint venture profit share or equity partnership if you can simply amend operating agreement or create a shareholders agreement and offer membership interest or shares to new person - without worrying about separating out other assets held by that same legal entity.

TL;DR : Generally better to have a separate and distinct legal entity for each business.