I am trying to move completely to Houdini but simple tasks take long time such as sewing UVs :/
There is so many bugs also like double clicking on the UV island is not selecting it you need to try so many times.
And sewing two islands is so complicated in Houdini

I am referring to manual UVing of an object.

In my opinion there's no point in using sew and cut tools built into Flatten SOP because it is way, way faster to simply mark seams with seamgroup'sselection mode.