It is actually quite useful according to people I've talked to that are knowledgeable in the subject. Essentially the real capacity constraint on roads is intersection throughput - by adding an additional lane, even just through the intersection to the other side, you increase the intersection capacity significantly.
Now in this case, given the mess of left turns and weaving caused by that turning movement from York Street - I expect that it doesn't actually make much of a difference. But normally, it would.
Has anyone else noticed the backs ups and weaving issues being created at York Street with people turning left? It has made going straight through on Lake Shore almost impossible. I used to drive occasionally from Strachan to Yonge on Lake Shore - but find its taking 15-20 minutes more now than it used to. Now I drive westbound on Lake Shore, get on the Gardiner at Jameson, and then exit at Simcoe to avoid the bottleneck.
The city needs to find a fix - maybe ban left turns at York St. if you are coming from the Simcoe ramp somehow?