question

>>I am making progress in understanding playfab, but I still don't understand the significance of the lobby system. What are they for?

PlayFab Lobby service is used to create a temporary grouping mechanism for players to play games together. It's frequently used with matchmaking after finding people to play with. For more information about Lobby, you may refer to Azure PlayFab Lobby overview - PlayFab | Microsoft Learn.

>>My game is an 1v1 multiplayer game, so is there any advantage to using lobbies in that case? Is there a problem with simply calling CreateMatchmakingTicket on each client, then getting the server information and connecting?

Since your game is 1v1 multiplayer game, there is no big difference to use Lobby or not. And there is no problem with the game matching method you use.

>>And I may implement a 5v5 mode in the future. If so, what are the advantages of using the lobby?

If your game has a 5v5 mode, and you want to gather already matched players to share some information, such as player configuration, before joining a game session, you can use the lobby service. For more information, you can refer to Use lobby and matchmaking together - PlayFab | Microsoft Learn.