Can someone explain like I'm 5, the practical difference between team members and visitors?

@Yoni Balkind 

I would like to create a few boards which I use to collaborate with clients. So I would like clients to have access and edit rights on these boards. 

As far as I can tell I can invite people to my boards as visitors and they can collaborate freely. 

The Visitors feature is not available on Free Plan teams. The only way someone can edit a board in a Free Plan team is if they are a member of the the team. ALL members of a Free Plan team can see ALL boards in that team, so unless your clients are not all a part of the same organization, you would not want to do this.

The only reason I can see to upgrade to team plan is that it gives me more than 3 editable boards.

After my previous comment, surely you now see that unlimited editable boards is not the only benefit.

But when I upgrade to team plan (1 seat) it only allowed me to add team members on the basis of a 7 day trial.

You don’t have to upgrade. You can also just create a new (paid) team:

Why would my team members have more privileges when I’m on a free plan?

As I mentioned before, there are additional benefits to having a paid plan - you can see a full comparison of plans here → https://help.miro.com/hc/en-us/articles/360017730233-Plans-and-features-available

Visitors vs. Guests

First, the Guests feature is not available on the Team Plan - it is only the Consultant, Business, and Enterprise Plans.

Before we continue to breakdown all of the pros/cons/caveats/etc., I would interested in understanding exactly how you need to work with your clients.

For example:

• Do you work with clients from different organizations, e.g., you need to segregate information for privacy/confidentially purposes?
• Will your clients need to create their own Miro board in your account? (Visitors and Guests cannot do this).
• Assuming you will be collaborating remotely, will you be exclusively using Miro’s vide chat or will you use using a standalone application, e.g., Teams/Zoom/Google Meet? This matters as there are some features that only Guests can do, e.g., Mention people in Comments; Lock/unlock content; set up Video chat, timers, and do screen sharing inside of Miro.
• Do you anticipate needing different access levels for a board, e.g., one person should be able to edit the board while another has view-only access - you could do this with the Guests feature, but not for Visitors.

Been a while since I have see this post and I have a note about the following:

Visitors are one-time & unregistered collaborators who can access the content of the board but cannot share it with other users and use certain features.

Specifically:

but cannot share it with other users

They absolutely can share the content of the board -- all then have to do is share the lnik (and password, if one was confiugred).