What happens when you disable a monitor/all monitors for a pool?

If you are in an Active/Standby scenario, then all your virtual servers are always served by the active node, thus after a failover they all switch to the new active node independently of whether the underlying pools are monitored or not.  

Monitoring is something tied to pool members and/or nodes, the VS is just ineheriting whatever status it observes from its attached pool. If you disable monitoring (pool and VS become blue), then the active F5 will just send traffic to the selected pool member without caring about its state, spray and pray, that is the actual disadvantage