Big Ads,
1) In transition, if our PG and SG are playing on a different man on offence, to whom they have on defence, there are a few more secs needed to find their man and good teams can take advantage of this confusion.
2) With a smaller backcourt (Delly @ 6'4" the biggest) teams with a bigger backcourt player are more likely to be able to take advantage of mismatches.
Now I'm not saying Delly or Mills have been bad defensively, but at times Mills lack of size in particular has been exploited.
What I am saying is that in an ideal world, the future Boomers team would find a bigger, more athletic starting guard that would address this weakness.
So if you interchange Delly and Mills at PG, rather than play both together, you open up that SG spot to a bigger, more athletic player.
That allows us to put some pressure on passing lanes with two long wing players, improves our ability to protect the defensive glass and hopefully also gives us a backcourt player who can drive and score in traffic in the halfcourt and also make the open three.
(A big part of the reason we get stagnant offensively is because in the halfcourt, neither of our guards is a serious threat to score at the rim, so teams can play up on them and force them to drive into trouble).
Of course, this all depends on Mills improving his PG skills, because as of now he is purely a SG with good ball-handling!