Good Morning Roger,

I use the syringe to prime the master in the vise when doing a bench bleed. This is helpful to get the piston bore full of fluid for when you start manually pumping the piston fully in and out to get full fluid flow and start building pressure.

Aster it is in the car I also crack a bleeder, use the syringe and help get fluid travel started before pumping the system (If needed) then bleed normal starting with the longest brake line.