in theory, it's necessary on the last board in the chain, however the boards are star-wired by default which destroys any noise-immunity provided by a transmission line.
If you have only one extruder, install the resistor.
If you have more than one, it probably won't make much difference unless you chain them instead of connecting them all to the mainboard, in which case only install the resistor on the last one in the chain.
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Wooden Mendel
Teacup Firmware