Would someone please be kind enough to explain what
design criteria would require holes in SMD pads?

Especially blind holes in SMD pads?
 

That's not a bad question, if you haven't done an "impossible" double-sided (active devices, both sides), way-too-much stuff on the board design. The design criteria might be:

1) Very high density, surface mount board, with lots of busses and lots of critical matched pairs, and matched groups.

2) A blind via board is very adaptable to putting the vias in the pads. These vias tend to be very small, .004-.010"; and only go .004-008" into the board. There goes the 'ol solderpaste into the via, my components don't get good solder joint complaints.

3) High pin count BGAs and QFPs can be prime candidates for via in pad designs.

As always, check with your fab house(s) and assembly people before proceeding down that path though.

Good luck,

Mitch
Sr PCB Designer
San Diego, CA