Well to me having a business partner in a company can be sometimes shaky but still on still "so they say two heads are better off than one" Also having a business partner fills in this gap in the organization or company cost savings, emotional support, additional hands on desk, additional capital, and the many important aspects of it responsible can be shared.
Having a business partner will lead to new opportunities and ideas and also someone you can share your burden with
The type of business someone is going into will determine if they need a partner for that business or not. There are businesses that are just good to be handled by one person alone until they have upgraded to the level where the person will need external help.
Having a business partner most times is mainly not just because of the money the person might be investing in the business, but most times the partner can also be because of the experience the person has in that field, which you necessarily need in order to take your business to the next level.