We used the linked reservation option for a family cruise last year on Oasis. It was great! I was able to get on and make reservations for the comedy show for the adults, Aqua80 for everyone (but 1 kid, long story, but too many reservations and 5 people in a room complicated the linking a bit), Laser tag, etc. it was easy to pull up and see who in our group wanted to do something, and see if there was enough space for everyone.
I was also able to help get everyone check-in times together because I had that access. It was especially helpful traveling with my parents who are technology challenged. I was able to make the internet and soda package reservations and they just paid for it. Super helpful for them. It was also helpful when figuring out shore excursions and CoCoCay things.
Side note: if you use a travel agent, you can't see payment dates, etc for linked guests.