Let's look at my great grandfather, Thomas James Corcoran. He grew up in Dillonstown, County Louth and was then sent off to America at the age of 26 to meet a cousin. The rest of his family stayed behind in Ireland. You can read up more about why he left here. He never came back to Ireland so the record trail would run cold if I only continued to research him in Ireland. My 3rd great uncle Peter Dougherty also left for America. He was born in Ireland but went with his family as a young boy to Prince Edward Island, Canada and then ultimately came to America to homestead.
I then think of our current generation where it seems like nobody really lives in the same place for long. From my personal experience, I grew up on Long Island, NY until I was 18. Then lived in central, NY at college and then back to Long Island for two more years following graduation. I then went back to central NY to live in Syracuse for the next 10 years. I'm now about to make another big move and go to Boston, MA. I wonder sometimes if anyone researching me years after I pass if they'll be able to trace my migration pattern. They would need to understand where I went to school and look at the FAN club to see that I had college friends in Syracuse, NY area (maybe one day Facebook will be archived and give some clues to who we associated with). Then I wonder what they think when they're looking for me in 2018 and I'm not in NY. I'm probably not listed in any city directory or phone book. And who would think that I would make a jump to Boston from central NY? I don't have any close family there.
Let's throw another wrinkle into this equation. I lived in Onondaga County, NY but my marriage actually took place in Madison County, NY in a small town called Canastota. We found a wedding venue there and there was no restrictions on where we got married in NY. My marriage certificate is actually filed at city hall in Dewitt, NY (in Onondaga County in a neighboring town near where I lived).
To leave a lasting legacy we need to leave some kind of paper trail. Type up the family history and include yourself before you donate it (or leave it set up for donation after you pass) to go to a historical society. Blog about your experiences while you're still here on this Earth and share the history. Oral history is such a valuable resource and the stories passed down capture more details than most manuscripts. There are people who knew your ancestors. Record their memories and say their names to keep them alive. Leave those bread crumbs so your story can be found.
What does your scavenger hunt look like for your descendants?