Not really relevant, whichever end you look from. For historical matches, I believe* they only use Y-DNA (direct male line) and mtDNA (direct female line), as Autosomal DNA (your typical Ancestry and MyHeritage tests) is too diluted after so many generations (ie. sharing mum's and dad's DNA). At such small amounts, pretty much everyone would "match" everyone else - but 99.99% would be false matches, and unprovable by other means. Also Y-DNA and (especially) mtDNA mutate at much slower rates than Autosomal, meaning it's feasible to estimate a date range for matches (ie. number of generations back to common ancestors).
* happy to be corrected.
