When dealing with family trees which include intermarried lines, there is this little problem with encountering duplicates. Only those whose trees include what's called "pedigree collapse" would need to keep an eye on such an occurrence. When it comes to the lines of descent of my mother-in-law's tree, that issue crops up a lot.
Hence, I'm always on the lookout for duplicate entries. Hers is a tree with multiple intermarriages, primarily because her family settled in one place and stayed there for, oh, a couple centuries.
Moving up the family lines, starting with my mother-in-law's own parents, it didn't take long to realize how intermarried the families in her Ohio hometown in Perry County had become. I'd work my way up one line—say, her patriline—adding all the children for each specific generation, then moving to the parents of that generation and their place in their own birth families. At some point, a spouse would get entered into the family line who had a double somewhere else in the extended family. Sometimes, second cousins would marry, or third cousins who perhaps didn't even realize the relationship. While I'm focusing on the Flowers line right now, I've seen the related surnames of Snider, Gordon, and Metzger get woven into more lines than one.
Thus, adding the siblings to each generation—those collateral lines—results in multiplied duplications. This is something I've had to periodically monitor, lest the proliferation of entries in that family tree become nearly twice the size it truly is.
While Ancestry.com's "Tree Overview" provides a Summary section which can be sorted alphabetically by surnames, it does mean requiring a visual scan of the list to spot duplicates. An easier method is to keep my Ancestry trees synced with my desktop-resident program (I use Family Tree Maker) and regularly run a check through that feature. There, I can easily determine whether I'm viewing a true duplicate entry, or simply a matter of several descendants all named after the same ancestor.
As for those namesakes, there are many. Names like John and Joseph, Catherine and (especially) Mary make me grateful for the advent of middle names. Many times, the differing dates of birth, or places listed, help differentiate between what otherwise look like duplicate entries. But sometimes, I encounter duplicates for which I have yet to confirm any of these secondary details, requiring another look to see whether a linking person—parent or spouse—can become the tie breaker.
While the tree-trimming can become cumbersome, it's a necessary step to ensure those remaining in the tree have their one place, not two—or multiple!—duplicate entries. Sometimes the threads of this family tapestry become so interwoven that I realize how much like a fabric a family can be, rather than simply the intersection between two disparate lines. In those tight-knit communities—whether in Ohio's rural coal-mining country, or far away in isolated mountain villages of other continents—that's what makes people lose the thread of connection and simply resort to saying, "they're kin."