I mean as a technology, for the average or home user it is a good thing. What it promise is that it save you power or in other words it doesn’t let your system waste power on things that is unnecessary.
If you’re a geeky kind of reader, you can delve into it more here to read about the sophisticated algorithms which is able to decide when a particular application is just sitting in the background doing nothing but eating up resources. This clever thing is here to change this bad behaviour, but maybe it can cause some issues in the audio world.
In theory this is a fantastic thing which is very beneficial to us, users. In practice though, several forums are filled with threads discussing the detrimental effect of App nap in OSX. As usual, some argue that this is root of the problem, other say that this can’t be a problem, but after you finished reading a few threads like this, it may be a good idea to take some basic steps in order to avoid any problem.
As far as I know, every software developer has the option to code its own app so that it doesn’t allow OSX to put it into the “nap” mode, though most of the times we don’t have the information about this, so it is safer to act, and disable the whole thing at once.
While there are small tricks to switch of App nap in the get info window, I recommend to simply switch it off system wide.
One way is to use some smart app like Coctail which can do much more than this, I highly recommend to purchase this smart little utility to keep your Mac in a good shape.
In the app you can find at the System/Misc tab the option to turn App nap off.
The other method is to use the terminal app and a command to turn App nap off completely. Pay very close attention to use the command properly, even one letter difference can render it useless:
defaults write NSGlobalDomain NSAppSleepDisabled -bool YES
It doesn’t really matter which method you use, the point is you won’t have to worry about a smart background algorithm which may interfere with your audio work. Remember that these technologies are created with a general user in mind, and with all the good intentions from the developer, they can still ruin our DAW’s stability.