Why would someone do this?
Although offsite guests can now make 30 day advanced FP+ reservations, there are still advantages to making a throwaway room reservation if you are staying offsite:
1. 60 day + advanced FP+ reservations for the length of stay of your throwaway room, including the check-in and check-out days, up to the number of ticket entitlements you have. Days do not need to be Even a one day throwaway room has a significant advantage here, which will be explained in a minute.
2. Magic bands (MB) for everyone on the reservation.
3. Free parking at Theme Parks for the length of stay of your throwaway room, including the check-in and check-out days.
4. Admission to Extra Magic Hours (EMH)
5. Advanced dining reservations (ADR) 180 days prior to check in for the entire length of stay ("180 +10")
Do I need to actually check-in?
With the advent of online check-in, most guests do not even show up at the resort. If you check-in online, your MB is already active and can be used for Theme Park parking, FP+ and EMH.