Many of us know this: You are on KDE version "from yesterday" and suddenly, everything breaks. Maybe someone broke the kompile or it is just a bunch of bad code that went in before your checkout and prevents the window manager from starting.
You learn from this mistake, you no longer install to /usr, but you create a dedicated user for your KDE programming fun. Soon, the next painpoints arise:
- you cannot test the display manager
- you cannot test the latest system-wide dbus stuff
- the complexity is just annoying
I kicked both ways to program KDE. I am now using a VMWare Server virtual machine for my programming. Got rid of all problems above. And the best is: I just broke KDE. No problem! I just revert back to the latest snapshot. I am so happy I took this way!