Can the guest use functions of premium owner of the board?

[Martina Třeštíková]

Does the guest (member of board) without Premium account have option to use functions of Premium member who own the board (such as add members who are responsible for the task in the list etc.)? 

[Rafael Dill]

Hi Martina, welcome to the community! Yes, a guest member can do all the Premium features on that Workspace because when you upgrade your Trello, you upgrade the Workspace and not the account.

So if a guest member has access to a Free Workspace, he will have only the features of a Free account, if the guest has access to a board on a Premium Workspace, he has access to all Premium features on that board. Keep in mind that admins and members have different permissions and in this response, I'm referring only to board members (or guests).

With Premium, you can set users to be Observers which has different permissions, as you can see in full detail here -  https://support.atlassian.com/trello/docs/adding-observers-to-boards/

Hope that information helps!