Two testscenes for showing the pros and cons of this technique.
The application computes Global Illumination, using Global Line Radiosity
The outdoorscene (enabled sun + skylight) converges a lot faster since the direct light distribution is a lot better and therefore light gets propagated a lot faster too.
In contrast, the indoor scene works still reasonably well when the sunlight enters the open window at a good amount. But, when only lit from emitting materials it takes noticeably longer to get a stable rendering (visible blotches).
Also, the indoor scene consists of considerably more triangles then the outdoorscene (see stats HUD in the screencaptures).