Recently there has been work on a specification to consistently group userspace application processes together through cgroups and make sure we all use the same slices names and conventions.
Given there is realistically only one cgroup controller out there the current discussions have been happening on systemd, with a draft specification here: https://systemd.io/DESKTOP_ENVIRONMENTS/
I wanted to cross post here as it's becoming an emerging standard and ultimately will be worth copying or at least referencing on freedesktop.org.
In short the idea is that every time we open a new graphical application it gets put into a new cgroup. This can improve resource distribution fairness, as well as making life easier and more correct for task managers, system monitors and alike. More information on the motivations can be found at my blog [1] or Benjamin Berg's Guadec talk [2].
Most applications won't need to change anything, but programs that launch other applications will need to be using relevant API.