the 'base' coat as you describe it is also often called a skim coat.  if you do it in the morning, you can do your glass coat later in the day.

the idea of the skim coat is simply to put a very light coat (often spread with a squeegee) to just block the pores of the wood...so when you do the later glass coat, it prevents the wood from soaking up all the epoxy and potentially leaving a dryed out area of glass.  this usually results in a lighter overall build and protects against outgassing (when during rising temperatures, the wood gives off air that gets trapped as little air bubbles int the glass/epoxy.

i usually do it becuase i like to keep my builds light....and avoid the having to babysit the next coat....looking for places that i thought were wetout but where the wood aborbed the epoxy...not leaving enough in the glass.  i also like to not have to worry about out-gassing.

it does add an extra step....and you can certainly get away with not doing it with no major problems....so its really a matter of preference and how you want to control factors like weight and out-gassing (e.g., only epoxy during declining temperatures)

h