Never unless I take on managing a team there. I managed Hibs on it and won the title once. Not a fun league since it's very uncompetitive and most teams have very low moral since they can get a decent run of form going without running into the old firm and whoever you will be managing. That league is stupidly small, and dull. Outside the old firm the players generally poor bar one or two, the match attendences are low and there is no money or good facilities to bring in young players. Theres not even a reserve league.
To make the SPL league interesting you have to mass edit the teams outside celtic and rangers, raise their attendencees, upgrade their facilities and give them a rep boost. I would of liked to make the league bigger but you can't. Personally I would stay suggest that players away unless you support one of the teams. You end up thrashing teams by 8 or 9 goals with midiocre players and get thumped in europe. Dutch and Belgium leagues offer more of a challlenge and have better teams and youth players and league format than Scotland if you want to play in a smaller league.