You don't really have a SF per se. You have a player that BB has suggested that SF is his best position. This position is actually calculated each week and can changed, based on his current mix of skills.
If he plays as a SG in a game, he is a SG for the minutes he plays at the position (a player can play multiple positions within a single game).
How your player developed would depend on his size and his age. If he is a 7'2 he won't get as much out of the JS shooting as if he were 6'2.
If I were focusing my training on guards, but had a younger SF who I want to improve his shooting, I would train JS PG/SG and use the SF as the SG in the training game. Or if I had some forwards that I wanted to improve their shooting I would train JS SG/SF and perhaps use a PF as the SF in a the training game (or perhaps a PG).