Difference between different resistor configurations with optocoupler
You are comparing two totally different versions it terms of input impedance. The one has 4.7k series resistor, while the other has 10k.
The parallel resistor provides faster turn off in case the driving circuit is open collector /or/ open drain /or/ high side P type transistor. Due to LED self capacitance (and the anti-parallel diode that is not present in your schematics), it continues to glow for a while even if was already disconnected. The resistor helps to discharge and thus the LED turns off faster.
You will find the version with parallel resistor for high speed pulse input in  motor drivers (although different values than you provided, typically is 1.1k). You won't find those for low frequency PLC input signals. Don't forget to put an extra anti-parallel diode for reverse polarity protection.



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