It would be really nice to be able to only have screens automatically switched off - as opposed to suspending the session - when running certain applications. In my case, this would be when I'm running a Handbrake encode for 4-6 hours unattended. At present, the user has to hop into Settings -> Power Management -> Energy Saving to be able to uncheck the Suspend Session box. It would b really nice to be able to get Handbrake going and walk away without having to go through the procedure I just mentioned. I'm not sure if it would be best to implement on a per-application basis or going by CPU usage, but this would be a very handy feature.
This is something that Handbrake should do itself. Many other apps already automatically inhibit suspend when they have ongoing tasks. I would recommend that you ask the Handbrake devs to do it as well. If you need to do it manually, you can do it more easily by clicking on the "Battery & Brightness" applet in your system tray, and clicking on "Manually block sleep and screen locking".