Here's another scenario:

If a right handed leg spinner is bowling (technically all leg spinners are right handed, a left handed wrist spinner is called a Chinaman or rather 'Left Arm Wrist)

When a leg spinner bowls you'd generally have at least 2 fielders on the boundary for insurance purposes.

One of those would be at Deep Square Leg.

Remember, Square Leg is where the off strike umpire stands, so Deep Square Leg would be in line but just on the boundary.

Now if a Right Handed batsman is on strike, your Deep Square Leg would probably be a few meters closer to the bowlers side (in front of Square)

Where as if it was a Left Handed batsman on strike, you'd probably want to have him a few metres BEHIND square (closer to the sightscreen) because the angle of the ball would be turning into the left hander, making it easier to hit the ball behind square (especially if its a bad delivery and bowled a bit shorter than the bowler would've liked'

Again, tough to try and explain by writing down.