The following are some points to remember:

• Don't perform the DML operation inside the Loop element. It will easily hit the governor limit, that is, System.LimitException: Too many SOQL queries: 101.
• You can only launch Autolaunched Flow from Process Builder. 
• A Flow runs in user mode and Process Builder runs in system mode. Let's take an example—if you are trying to update an Opportunity, the next step would be as follows:
  • If you use Process Builder: If the running user doesn't have access to the next step field, Process Builder will be able to update it.
  • If you use Flow: If the running user doesn't have access to the next step field, they will get an error.

• The DML operation on a setup object is not permitted at the same time as when you update a non-setup object (or vice versa). If you want to do that, then use a time-dependent action.
• The total number of records Flow can retrieve using SOQL queries is 50,000, and only 10,000 will be processed as DML operations.
• You can have up to 50 versions of a Process, but only one version of a Process can be active.