The goal of SSTU is to provide low part-count solutions for common designs, in a semi-realistic model/art style.
The KSP forum thread may be found at: http://forum.kerbalspaceprogram.com/index.php?/topic/117090-sstulabs-low-part-count-solutions-orbiter-landers-lifters-dev-thread-01-30-16/&page=1
This is accomplished through module and part integration (e.g. integrating heat-shields, parachutes/etc into command pods), semi-procedural parts (modular/customizable fuel tanks -- no more tank-stacking), and pre-built multi-engine clusters (need 7 engines on your rocket? got you covered...).
Essentially these parts are solutions to part-welding with incompatible parts, with the goal of reducing CPU overhead and enabling you to actually -play- the game with your ships, rather than watch a slideshow.