It does defeat the purpose, doesn't it?
Now, interesting point. When one of my Pruitt cousins goes back 8 generations it says something about my research and his research as well as the fidelity of long dead folks. Sometimes when you knew, for instance, without hard documentary proof, that a Cochran ancestress was a Cockerham, it's good to see someone else's DNA going a generation or two earlier than her, safely into Cockerham land. It may solve some problems just incidentally. When there are shared ancestors but also another familiar name, Bandy, for example, I may someday find out if the Ann Rogers/Rodgers who had charge of a young Bandy boy and took him from Tennessee to Arkansas and raised him there was herself a Bandy, caring for a little brother. Least knowledge of all: about the Parkers.