Example of using alternatives to each

[nick-youngblut]

As the nextflow docs state:

Input repeaters currently do not support tuples. However, you can emulate an input repeater on a channel of tuples by using the combine or cross operator with other input channels to produce all of the desired input combinations.

It would be great to have >=1 example of using combine and cross in this manner. For example, what are some (common) scenarios in which this is necessary?