The Road Not Taken by Robert Frost compares two paths in a wood which go in different directions. The reader recognizes the symbolic message in the descriptions and can relate to the narrator's dilemma as he ponders his choice and laments the opportunities he may be missing on the other path. The whole poem is a metaphor for life as a journey with the narrator comparing himself to a traveler who considers how the choices he makes now will affect outcomes in the future.
In terms of its metaphorical value, the poem also serves as a warning to the reader not to dwell on or obsess over missed opportunities but to learn from the narrator's mistakes and actually relish decisions made rather than living in regret and uncertainty. Furthermore, Frost wants the reader to realize that not all decisions are life-changing- note how "the passing there Had worn them really about the same," indicating that this particular decision may not have made much of a difference in fact, although the narrator would not agree.
In terms of individual comparisons, there are not many and the real value lies in the fact that Frost uses something tangible to get the message across. Frost does use personification to compare the two paths when he talks how one path has "the better claim" and both paths "lay in leaves" as if comparing the paths to people. He also compares the path that the narrator does not choose to a keepsake, something that he can put away "for another day."