I know a little about this but not an expert. I have owned a sigma and a magna but have not removed the balanace shaft.
Removal will cause the engine to shack a little more. You can get the kits from repco appaerently.
If you balance the engine well during a rebuild it is unlikely that you will see any adverse effects. And you will see a slight power gain.
Advantages is less timing chains and a little more power. Little less weight (these things are heavy barstards and there is two of them and the chain)
Disadavantages are engine will shake a little at idle and higher revs if not balanced. Lot of work. Kit cost $250+. You have to block up oil galleries some how, some people have had problems in doing this resulting in low oil pressure. Again lot of work. If you are rebuilding an engine however you are crazy not to do it.
For some reason probably economical mitsubish feel the need to put these shafts in proably because they did not want the cost of balancinf a big four cyclinder but every other jap engine provided has not had the need to put them in a 2 litre engine! and porche has some big fours and do not have the need for such shafts.