The unwritten rule is, "If a feature is not on by default", there is a specific reason, so do not turn it on unless you test it in the lab with all your clients. There are some features that only provide benefit to a subset of clients, but to the detriment of others. This changes depending on manufacturers and drivers, so it is impossible to keep up with this list.
As I say that some clients have problems with CSA and 802.11h, those manufacturers might have fixed those issues and I could be wrong. Is the performance benefit worth turning it on?...no.
As more and more devices depend on wireless mobility, the more features and knobs have been put in to take advantage of those devices, but the more conservative administrators need to be to ensure that nothing breaks.
In many TAC engagements if a customer is having alot of trouble with his wireless and it cannot be pinpointed, the typical strategy is to go back to the defaults and work from there.