Mac 0SX 10.11 (El Capitan)

[Bobbsy]

Mac users may wish to read THIS from Native Instruments before considering an upgrade.

Although this article applies specifically to Native Instruments, I've heard of similar problems with a number of DAWs with faults such as plug ins no longer working properly.

You have been warned!

 

[Steenamaroo]

Good info.
Just to add to it, don't upgrade your operating system unless you absolutely need to for some reason.
Even then, clone your current system first. (two clicks in disk utility)

I don't mean just this time; I mean in general. You're asking for trouble.