"Account linking" is the act of associating a Kintone account with a guest account when a user with a Kintone account is invited to a guest space in a different Kintone environment as a guest user.
By linking accounts, users can access guest spaces they are invited to from the main page of their own Kintone environment, even though the guest spaces are in a different Kintone environment. In addition, since the guest account linked to a user's Kintone account is not counted as a licensed guest user, the guest account for the user becomes available for free.
Actions by guest user: Linking your guest account and Kintone account

Ejemplo:
Este ejemplo explica un caso en el que compró la licencia para cinco usuarios invitados, de los cuales tres están en uso.

• Si no hay cuentas vinculadas: el número restante de usuarios invitados disponibles es dos.

• Si una de las cuentas de invitado está vinculada con una cuenta Kintone de un entorno diferente: el número restante de usuarios invitados disponibles es tres.

Note that, even if a guest account has become available for free as a result of account linking, your billling amount will not change automatically.
If you want to reduce your billing amount, you need to reduce your number of guest accounts.