There are upsides and downsides to JVs.
I'm thinking here the OP is meaning JVs in general ( as opposed to the JVs section on here ).
Upsides include you bring together your own skillsets, finance could be part of the package. You dilute your financial exposure, should the venture fail.
Downsides; you're no longer in control, you have to share profits etc.
Watch Dragons Den or Sharktank on tv for an insight as to how to get screwed over by business angels ( the people want to offer 10% for $100k and the last Dragon screws then down to $100k for 49% ) But also how these people can help.