To light the LED, using the resistor to define the current, it doesn't matter which order they go in.
There may be some other non-electrical reasons for preferring one over the other in specific circumstances.
For instance, if you connect the LED directly to the PSU +ve, then accidentally shorting the LED to ground, as you might do with an untidy breadboard, will kill the LED. Resistor to PSU will be safer. This situation is asymmetric because shorts to ground are more common than shorts to PSU live when you're clowning around on a breadboard. This may be significant in your lab instructions.
There are other situations where multiplexing LEDs, or running them at various currents, is made easier by one or the other connection. This is asymmetric because of the popularity of low side switches, things like ULN280x and their ilk, which people tend to use for driving LEDs.