Systemd programming part 2: activation and language issues

I think the separation into the sections is more for clearifying what the directives apply to.

Directives in [Unit] apply to the dependeny tree and define general properties of the unit.
Directives in [Install] are only used when running systemctl enable/disable and have no other direct effect.
Directives in [Service], [Socket], ... define the behaviour when the unit is run. And as the allowed directives are different between unit types the sections also are named differently. This little redundancy may also help catching copy&paste errors between unit files.

Sections like [Exec], [Kill], ... would only group some related directives without providing context. Currently it would also split the execution environment directives and the Exec, ExecStartPre, etc. directives into different sections.