If a site has 3 practically identical pages then crawlers would have difficulty identifying the canonical version of the page, which would prevent the correct version from ranking as highly as it should. In explaining the equity advantage of a single distinct page over a set of duplicated pages, is people will be linking to the same URL instead of link equity being spread across many. Once the issue has been corrected ten links would be pointing to one URL instead of one to each of the ten copies, thus giving ten times more powerful link equity. Due to the content being more unique, it also has less of a spam factor / a higher content quality score. Note that if the pages were slightly less unique but still too similar for desirability, ‘keyword cannibalisation’ becomes the issue.
One potential solution would be to use the rel=”canonical” tag to identify the correct page, this is the right solution if separate pages are really needed for site functionality or personalisation, but often it’s done in error due to some versions being a bit older, or the site code being messy, in which case the best solution (where possible) is actually to pick a canonical (preferred) version then do a 301 redirect from the others to the chosen one. Canonical tags consolidate equity well but not perfectly, whereas 301 redirects are more definitive and universal.