The nice thing about this is that previously you may have hesitated to mess around with something with complex history if you thought it might go off and lock things up for some unknown length of time.

Having the ability to cancel with the next beta means that you don't have to hesitate like that anymore. It's still possible that it might take some length of time to finish calculating, but if you don't want to wait you can bail out, you're not just stuck there. So you can feel more free to experiment.

The only thing that is not quite "perfect" is that you do have to wait for history to be calculated after you finish any particular operation. Like if you drag a control point, history needs to be updated when you release the mouse to finish the drag. Although you can cancel it, if you want to accept that edit and do some more, you still need to wait for it to finish before you can do the additional operations.

Ideally it would be nice if you could go on to do several other operations, like drag some other points, etc..., without waiting for the update at the end of each separate operation.

It's going to be pretty complex to get that to work because of issues like what if one of your additional operations is to delete the curve... So that full level of fluidity will have to wait until a future version.

- Michael