Since Mavericks there is a feature called Nap app.
For some reason it can be better to prevent an application to take a nap.
You can disable this for a specific application.
The Manual Solution:
Mavericks comes with a dreaded feature — App Nap – that is designed to save battery live and be energy star compliant. Fine for some apps – but it doesn’t really work if you are using Studio as a web server. You can manually turn it off by: – doing a ‘get info’ on Studio and – clicking the ‘disable app nap’ feature.
you’ll get all your studio horses firing on all cylinders even in the background – which is what you want.