Pretty much all of the efficiency metrics revolve around shot attempts - FG%, eFG%, TS% etc. Each has their weak points and none take into account the value of all three of the different shot values - 2pt, 3pt & FT while only TS% takes into account the actual points scored by the player. It also includes a somewhat arbitrary multiplier for free throw attempts.
 
Why do we not measure the efficiency of a player based on points only? So basically, the amount of points a player attempts vs the amount of points he eventually scores. To me, the two metrics reflect the difference between great scorers and great shooters, they are not always directly proportional.
 
Example, a player attempts 10 two pointers, 5 three pointers and 5 free throws per game throughout a season. He ends up averaging 5 made twos, 2 made threes and 4.5 made free throws. The total points he attempted was:
 
(10 x 2) + (5 x 3) + 5 = 40 points
 
He succeeds in scoring:
(5 x 2) + (2 x 3) + 4.5 = 20.5ppg
 
His scoring efficiency is therefore:
20.5/40 = 51.25%
 
His shooting efficiency, based on TS% is:
20.5/((15 x 2) + (4.5 x 0.88)) = 60.36%
 
Applying scoring efficiency (ScEff) to some all time great scorers/shooters:
 
Michael Jordan -
TS% - 56.9%
ScEff - 54.1%
 
LeBron James -
TS% - 58.8%
ScEff - 52.6%
 
Steph Curry -
TS% - 62.8%
ScEff - 50.7%
 
Larry Bird -
TS% - 56.4%
ScEff - 53.4%
 
Kobe -
TS% - 55.0%
ScEff - 49.7%
 
Harden -
TS% - 61.0%
ScEff - 50.3%
 
Wilt -
TS% - 54.7%
ScEff - 53.4%
 
Interestingly, Jordan moves from the 4th best TS% of that 7 player group, to 1st place in terms of scoring efficiency. Curry goes from 1st to 5th. Jordan is widely regarded as the greatest scorer of all time and Curry as the greatest shooter of all time. Kind of apt that they would swap places on these lists.