There are a lot of reasons for a cooperation.
However, there are many cooperations which fail. If you are looking for a strategic partnership e.g. in the form of a joint venture, legal firewalls should be your highest priority. Take a few precautions, e.g. by performing a due diligence prior to jumping into any adventure. Moreover, potential risks should be reduced to a minimum by agreeing on appropriate terms and conditions in the cooperation or joint venture agreement which duly cover your interests.
Finally, your potential partner will gain a deep insight into your business activities and/or trade secrets. Make sure that such insight cannot be turned against you during or after the cooperation. In those cases appropriate legal agreements are similar to insurance policies which - in a worst case scenario - might provide you with a crucial advantage.