Maybe you don't quite grasp the needs of a DAW and how they differ from any other PC - or Mac - usage other than maybe serious video/film editing.
Windows is, of course, a multi-tasking system. If there are multiple applications running it allocates resources to each of them. This means there are brief periods when an application is not getting Windows full (or any) attention. The more applications runnign, the less attention each, includiong the DAW, gets.
Now, the thing about DAWs is that they require as near to real-time computer operation as possible. If you have an ASIO driver buffer set to a latency of, say, 10 milliseconds (which is pretty typical for someone monitoring audio through the DAW as it is recorded) that means that if for any reason there is a period longer than 10 milliseconds where that buffer is not being topped up you get audio dropouts, cracking, all sorts of stuff.
Running e.g. wi-fi and a DAW at the same time can in some setups cause big problems because many wi-fi drivers hog cpu/PCI bus time for long enough to allow the ASIO buffer to overflow. That is not Cakewalk's fault, or Ableton's, or Steinberg's. It is down to the wi-fi driver and how the OS interacts with it (Macs don't have a problem running their wi-fi and a DAW, and PCs often have fewer problems using cabled ethernet). There are other drivers that can have the same consequences.
If you let drives go to sleep, then when Sonar needs to access a drive Windows that drive will very often take long enough to fire up that the ASIO buffer overflows = crackling and dropouts. Putting the screen to sleep means that when you wake it there's a bunch of driver and video subsytem activity. Which distracts Windows from keeping up with the DAW.
I can turn the screen off, or let it sleep to blank and recover from it most of the time by the way. But I don't try running multiple VMs or pretty much anything else either at the same time. If you want the maximum possible multi-taskling smoothness while running a DAW go buy a Mac. Seriously. I've an i7 MacBook Pro that has around half the speed of the sig PC and can run Logic Pro and reliably download stuff at the same time. Which that PC can't, especially using wi-fi. So long as I limit the Logic project to very lightweight plugins (no synths or samplers) and very few tracks. I hit the maximum possible cpu usage before having to freeze tracks a long time before the PC does though.
PCs can make great DAWs, but setting a PC up as a DAW is not trivial and they need tuning for it and some consideration of the real-world constraints.