Differences between recurring meeting with no fixed time and personal meeting?

Great question. Your Personal Meeting Room is reserved just for you. It is an easy way to start an instant meeting. You can schedule a meeting with your Personal Meeting Room. The meeting ID is the same. The issue with the Personal Meeting Room is it is accessible with the same meeting id and link. So, if you have back-to-back meetings, and people hard your personal meeting id, they may join when you don't want them to.  I suggest using your Personal Meeting Room with close friends and family. I also lock the room after the person I want to meet with joins. 

Now, a recurring meeting with no fixed time can be set up to use your Personal Meeting ID. I don't recommend you do that. Let the number be generated automatically.  You still could have the same issue with users joining when you don't expect it, but this one is easier to change. In fact, I have a recurring meeting, but I change it every three months. You can even have multiple recurring meetings with no fixed time, but you can only have 1 Personal Meeting Room.  You could have a recurring meeting for client A and a different recurring meeting for client B. 

They are very similar, but only use your Personal Meeting Room for close friends and family, and use recurring meetings for other users is what I suggest. 

I hope this helps. I added a couple of screenshots. Please click Accept as Solution if this answers your question.