Flanking strategy is not just send one guy alone to either die or get behind the forces. The flanker starts on the far side of the map, which requires a somewhat high PS. Now you read the opponent, if he starts to move toward your flanker, your flanker needs to be agile enough to escape fire i.e. barrel roll and boost or move fast enough to avoid arcs, like a 5 straight. Flanking is not a suicide mission. It's to create a tough decision for your opponent and an advantage for you. If that flanker gets behind the enemy squad, it gets an easier life that it might otherwise not have had. Pure Sabaac is almost always the first target priority, whether in a squad, or on his own. So making him a flanker now gives your opponent the decision to turn his back on your entire force to kill Sabaac, or let Sabaac live and do some major damage behind your forces.
What's the difference?
Turning your back on the rest of the enemy squad means you are going to have to kturn,etc. after destroying the flanker, putting you at a disadvantage that next round, and the squad could have a ship like the Upsilon that prefers ships not getting behind him, so while you chase the flanker, it provides a 4 attack primary to get more shots.
Here is a great example from Xwing Junkies. Go for Sabaac and let Redline fire missiles, or go for Redline and let Sabaac rip you apart?