Originally Posted by TheBlackCat
Second, twinview does not have all the functionality present in randr. Ignoring the fact that it does not integrate at all with the numerous screen configurations utilities present on modern Linux systems, all of which use randr nowadays, it also lacks basic functionality like being able to set the screen configuration on login. You have to edit your xorg.conf to get that, which means you lose a lot of flexibility and it means you need root access. There is no user-level way to preserve your screen configuration between sessions with twinview.
There is a perfectly well-functioning graphical utility called nvidia-settings which lets you set your screen configuration. This utility can even create an xorg.conf with your current configuration. The only part which is at root-level is the writing to xorg.conf part.
The other options that can be configured via nvidia-settings are actually stored in your ~/.nvidia-settings-rc file. These settings can be loaded by making your WM or DE call "nvidia-settings -l" on login.
nvidia's configuration is also exposed at some level. Hence there is this utility called disper (look around in this forum) which is a command line utility that can change your resolution on the fly (for example on login).
It is entirely inaccurate to assume that a large portion of xrandr functionality is missing when you use nvidia's drivers.