Even Rush seems to be unaware that a quorum could not have been established without this action. The Demons were boycotting at the time for the vote and no business could be transacted without a quorum.
Could have changed the rules.
BTW, the US Constitution, Section 5, clause 1, of the Constitution stipulates that “a Majority of each [chamber] shall constitute a Quorum to do Business”.
It appears the Dems used Flake as a tool to achieve its desire for a delaying FBI supplemental investigation, but it probably backfired on them.
Re the quorum and vote: IMO Grassley didn't need either in order to advance the ball and any business that was transacted could have been ignored by the senate.
However, both McConnell and Trump immediately agreed to Flake's stipulation as an effective means they could control of resolving any lingering doubts the R fence-sitters may have.