I begin using them more, and more, and I find them useful for generating certain images with patterns.
Like, almost every commands that ends with index2list are candidates for this.
rep_permutation_index2list => Generates permutations at lexicographic index. So, 3,0,1,2 or 2,0,1,3,4, and so forth.
rep_npr_permutation_index2list => Above, but only used for selection of some objects instead of all
rep_r_permutation_index2list => Like the first one, but it has repeating cases
And others too.