Of genetic genealogy's 3 tools, 810/1197 of our project members have Y-DNA results, 497 have mtDNA results, and 561 have regular autosomal results, which FTDNA calls 'Family Finder'.

24 years of genetic genealogy has revealed this population descends from about 15 prominent Y-DNA lineage groups, each with their own clear common ancestor, who had a unique distinctive heritable DNA mutation. 
It's good to know which of the 15 is your family's strictly paternal son-from-father Y lineage, in which surnames are inherited, to be able to distinguish your family's lineage from another's with identical surname (but unrelated Y lineage). 
These 15 genetic lineages branched off from each other in prehistoric times, while surnames began about 850 AD in Ireland and 1066 in England, so the 15 lineages are valuable for fundamental differentiation of the strictly paternal lineage
and ancient fundamental back-story and sorting, but for traditional genealogy these last several hundred years Y mutations since 500 AD and more distinctively characterized recent groups are whats important for genealogy. 

The first six Y lineages branched off about 2500 BC in northwest England, with 73,819 Y-testers to date, & are thus labeled insular; 'of the island':
1. R-DF21 has 9,575 DNA tested descendants in 7 now-known descendant lineages