If you have more than one Roku player in your home, linking multiple players to your Roku account ensures that all of your installed channels are synced with all of your Roku players.
If you have multiple members in your household who want different channels on their respective Roku players, you can link each player to a different Roku account. For example, one account for the kid's room, and one account for the parents in the living room.
Subscription channels, such as Netflix & HULU, can be used across different Roku players, even though they are linked to different Roku accounts.
Each Roku player may only be linked to one Roku account at a time.