Default extrusion multiplier .9?

[goopyplastic]

I curious why the default extrusion multiplier is .9 is this on purpose for a particular reason? that would seem to be a lot of under extruding.

[Simplify3D]

PLA usually requires an extrusion multiplier in the range of 0.85-0.9. ABS plastic is usually closer to 1.0-1.1. The software will actually change the extrusion multiplier based on what material you select to try to give you the best starting point possible. Different extruders can behave differently though, so it might require some slight tweaking to get the best results possible.