South circ traffic turning left from London Rd for instants, is currently stopped for 2 phases - once to let the Dartmouth Rd traffic across and once to let pedestrians cross from the island outside WHSmiths.
If people are crossing the whole width of the road instead, or somehow X-crossing this T-junction, then the traffic will wait for longer.
The only way you could possibly slow the traffic by less is by making the pedestrian waiting time longer.

Of course in the future we may indeed get quite a few all-stop sequences every day: the Morrison's alcopop monster delivery trucks will need a few minutes to reverse in and out of Havelock walk, and all the traffic will be stopped then. Huzzah!