Hello Giuseppe,
Adjacent Channel Support needs to be enabled if you are running ABAB frequency reuse scenario.
If you are using Adjacent channel with no gaurd band you need to enable this parameter on AP. Also note Adjacent channel Support needs to be enabled only on specific cambium equipment or radios. (3.6 GHz 450/450i AP and if there are any 450b SMs in 5 GHz network then on 450/450i 5 GHz AP).
Let me know if you have more questions or need additional explanation.
Thanks
Dhaval