The reason for this is to get some of the commission you pay these sites back by adjusting the rates feed to these channels.
ie adding an additional rates or stopsell to a specific OTA for Example: Booking.com only
Go to Resonline Home Page
Select Distribution - in Setup towards bottom of screen
Select the Channel from the website list (for example Booking.com)
The middle column on the Mapping Details tab is the Rate Adjustment column.
Click Fetch rooms
Then add the percentage you wish to add to each package/rate plan you wish to increase (for example to add 10% enter 10 in this field)
Click Save changes
Click Fetch rooms again - this will send a quick update - rather than waiting for the scheduled update
Click Save Changes one more time.