Last year, when multi select option sets were released, I wrote an article about this new data type and how it will be displayed on the form. You can find it here. Recently, while working on a project got a chance to work with multi select option sets and found out that there are few limitations in using multi select option sets.

• Create/set a multi select option set in a business rule – No way we can use/set a multi select option set in a business rule
  
• Create/set a multi select option set in workflow – not available in workflows either to check condition or to set the field value.
  
• Create a JavaScript condition – This is possible.
  

  

• Set field values through a JavaScript
  

  
  

• Multi-select option set can’t be used in the Form Head Section
  

Hope this helps.