In the last couple of years online poker bet sizing seems to have shifted to cbetting 1/3 pot on the flop and then barreling with a pot size turn bet. (well at least at NL200 zoom, this seems to be fairly common sizing from a preflop raiser).

Does anyone have any ideas about the theory behind this?

I understand it causes the villain to defend a wider range on the flop, but why is this good? and why the turn size pot bet?