Is there a convention as to placing a resistor before or after an LED?
Consider the possibility of a momentary short from one of the LED leads to ground (ground could be connected to the chassis)- perhaps it causes no problem if there is a remote resistor connected to Vdd but, if the LED is connected directly to Vdd, the short instantly destroys the LED. Or it shorts out the power supply. 







simulate this circuit &ndash; Schematic created using CircuitLab

There may be other similar situations you can come up with. But really electrically it makes little or no difference one way or the other until you invoke such possibilities.