Hi,
when I open a project with around 100 scenes in a few folders which are displayed full-blown in the Outliner, this takes Scrivener about 30(!) seconds to start. And even after this, navigating in the binder is a pain until I traverse all folders (some caching effects seems to kick in then). All the scenes have barely more than 20 words of text, only synopses, document notes and a handful of keywords each. I am running the project from an SSD. I have no backup option selected.
This was really annoying. My workaround was to collapse the folders when closing the project, so that Scrivener only had to display a few elements in the Outliner on the next start. However it then took frustratingly long to open the folders and get to work. Then, accidentally, in the options I deselected “Show start panel when there are no projects open”. From then on the same project took Scrivener 3 seconds to open, 10 times faster! 
Even navigating through the binder seems to be smoother from the start.
Has anyone else encountered this behaviour? Maybe this is something to investigate, because I cannot imagine why this seemingly innocent option should have such a tremendous performance penalty.
BTW: The Linux version does not show this strange behaviour. Opens in a snap with any option (Sigh).
Regards,
Linus