Last week I discovered the usefulness of the o line in an obj file. I had to bisect a complex set of objects and I couldn't do that because all of the g groups and no o object. So I added the line manually and it still didn't work until I flagged all g lines as remarks. That gave a single object in Blender but of course had the disadvantage of no more g groups.

Rereading the posts in this thread I went looking for the gear to change settings when importing and after I switched of groups just the o line was enough to allow selection of a single object, which I needed for bisecting and still retain the g groups.

Big vote here to add o line(s) to the obj export. I manage to create very complex furniture with just SH3D but there a few things it can't do that sometimes are needed.