Here's a link to the day9 daily on this build
This style worked because of how efficient mining is in sc2 with worker stacking. If you are on 2 bases, with 60 workers, (3 on each mineral patch, 3 on each gas), your income is only marginally less than an opponent on 3 bases with soft saturation (2 on each patch, 2 on each gas). As a result, you could just camp on 2 bases until you obtained a large enough army to secure your third base- and once you secured the third base, you could just transfer workers and be on equal economy to your opponent while having had the advantages of remaining on 2 bases (mainly an easy defense).
Since there are some new changes coming to LoTV, (where some mineral patches are getting extra minerals), I am wondering if this style will become relevant again in the PvT matchup.
Because you now have more minerals per base, I wonder if camping on 2 bases while getting up some fast upgrades will be viable in PvT.
With the mothership core gone, I certainly feel more comfortable defending 2 bases vs 3.