As I talk to young entrepreneurs, partnerships are a common topic. 
There seem to be a lot of questions about when and why to take a
partner.  After 30 years of watching partnerships (and being involved
in several,) I have strong feelings about the subject.

When my son came to me a few weeks back asking if he should take on a partner here is the advice I gave him:

One good reason to take on a partner:

1.    Take a partner only when they bring something to the table you absolutely can’t or won’t bring. 
This often takes the form of money.  If you don’t have the cash to do
what you want (and the bank won’t help,) you won’t get far without a
money man.  The problem with that is the money man often takes control
of the business (obviously, to protect his investment.)  At that point,
you are no longer in control of your own destiny, nor can you direct
the business without considering partners.

Another thing that partners bring (besides money,) is expertise. 
For example maybe you’re bringing on a financial person, so you can
focus on marketing (or vice-versa.)  Sometimes those things work.  But
often times you end up saying, “Wow.  I’m on the road 80 hours a week,
and you’re sitting at your desk 8 hours a day, and sleeping in your own
bed, how come we’re equal here?”  Then things start to deteriorate.

A bad reason to take on a partner:

1.    We’re buddies and we provide each other a lot of mutual support. 
From my experience, the best way to ruin a friendship is to form a
partnership with your friends.  Of course  there are many cases where
friends go into partnership and do great.  But in the majority of the
partnerships I’ve seen (and I’ve seen many) friendships are more often
destroyed by partnerships gone bad than made stronger.

A good exit strategy:

1.    The best partnerships have a well-defined exit strategy for everyone concerned.  What
does that mean?  Well, what happens if, “this town ain’t big enough for
the both of us?”  Who leaves, and how is the price determined?  While
there are as many exit strategies and means of determining a fair price
as there are businesses out there, here is the one I particularly
like.  If you offer me a price for my shares, and I don’t want to sell,
I have to be willing to pay you that price to buy you out.

For example, if you offer me $10 per share for my shares, you have
to be willing to sell your shares for $10 each.  What that does is keep
one partner from offering a low-ball figure to another.  It ensures
that you start the negotiations at what is more likely a fair price.

This is a complicated issue (ask any attorney,) so this isn’t
intended as the definitive treatise on partnerships.  Rather, it’s just
a few random thoughts, that will hopefully get you thinking.  The more
things you negotiate up-front in a partnership, the less grief you have
on the back end.