Pro's and Con's to adding DOI to theses
From the ResearchGate website:

Advantages:


  
  Make your research citable. DOIs provide information on where your work can be found online. They are guaranteed to never change, making them a great way to provide a reliable link to any of your research.
  Showcase all of your research. DOIs provide the ability to find all publications associated with a single author, including research that hasn’t been published.
  Put a date on your discovery. DOIs include the publishing date of your research, to make sure you get the credit you deserve. 
  


Disadvantage:


  Once a ResearchGate DOI has been generated, the research cannot be edited. Instead, you should remove the research completely, re-upload it with the edits and then generate a new DOI.




Also see:
Should I include a DOI/website URL for a publication in dissertation bibliography?