The 8-Degree Angle and Return Loss
SC/UPC (Blue) has a flat polish with return loss of roughly -50 dB. Reflected light bounces directly back into the laser transmitter.
SC/APC (Green) features an 8-degree angled end-face with return loss exceeding -65 dB. Reflected light leaks harmlessly into the cladding rather than back into the optical source.
In digital cable TV (1550 nm RF video), reflections cause severe screen pixelation and ghosting. This is why all CATV video equipment mandates green SC/APC connectors.