The nice thing about scanning either by the voter or while the voter is present is that spoiled ballots - by stray, faint, or partial marks, or overvoting for too many multiple candidates -
are reduced to near zero, and are replaced by
fresh voter-marked ballots, which simplifies all later
tabulation, and reduces confusion and challenges about
mis-marked ballots, thus increasing voter confidence in
the whole election process.
Anyone who is interested in election processes should
volunteer to work an election, either helping operate a
polling place, or as a poll watcher, or similar. This
is one of those areas that looks simple, but has a lot
of difficult edge and corner cases. I've been a poll
worker and a registrar of voters, and it is not as simple
as most people would think.
+1 Emphatic agreement that everyone should work the polls a few times. A lot the silly rhetoric would be quickly mooted if the belligerents had direct experience.
Sorry to pendant, because I know you already know this: some jurisdictions have (selectively) disabled the second chance feature for spoiled (or unreadable) ballots, effectively disenfranchising voters.
Anyone who is interested in election processes should volunteer to work an election, either helping operate a polling place, or as a poll watcher, or similar. This is one of those areas that looks simple, but has a lot of difficult edge and corner cases. I've been a poll worker and a registrar of voters, and it is not as simple as most people would think.