The lasso and polygonal lasso tools in the Select and Mask workspace create aliased, jaggy selections that are nigh unusable. The workspace options on the right (Smooth, Feather, Contrast) don't help remove this aliasing either, as shown in the screenshot:
Top: Selection made with normal lasso tool with antialiasing option (outside Select and Mask workspace)
Other three: Various experiments with the settings inside Select and Mask trying to fix the aliasing. It produces inferior results, because the original selection was aliased. Especially noticable along the bottom edge.
Please, add the option to have antialiasing on the lasso tool in the Select and Mask workspace.