Again, saved state. In my work projects often go on hold for months or years - I might need to come back to a project and pick up where I left off even though in the interim I replaced my primary computer, browser, and production software.
And in my writing side projects, I may leave a project for several months. So that's where I realized the value of VM's - the one's I use have survived an upgrade from XP to 7 with the same open windows and without any software reinstallation (and of course without any recreation of bookmarks). I'll add that they are also descendents of previous virtual machines used for the same purpose but different projects. It is more efficient from a workflow perspective to have six copies of Open Office each pointing to the relevant context than to reconfigure one copy each time the context switches.
To put it another way, the way in which one develops software projects from a custom starting point and the way in which references persist across IDE sessions during a project due to saved state are not unique to software development. They are indicators of the features which facilitate efficient project execution timelines.