The information that KMK gave is not 100% accurate.
Some resorts will charge a private event fee to those booked outside the group block. Palace Resorts does. Also, resort that have any "unlimited events" or private events complimentary are usually complimentary to those booked through the block so guests that are not booked through the group block may be out of luck.
This is especially true at resorts that have wristbands. Or if a resort sees that 30 guests have booked through the broup block, and will do a setup for 30 guests, but if you have 15 not accounted for, they may not have a place to sit or worse than that, YOU may be on the hook for the extra fees.
Also, if guests book outside the block they usually do not apply towards any group amenities that may be available to you.