The number one reason to use sources is time. I just spent two days trying to verify something in my own family tree. I decided to look at going back a generation in a line I rarely work on. Time is a major factor in rarely and also a brick wall.
The first thing I did when picking up the neglected line was to type the name of my ancestor I was certain about, into the internet, yes she came up with the same parents. When I looked further to find her grandparents I discovered that quick internet search was not a match to my family tree as she was married to someone else. Her birth date was the same on two sites but not a third. Her marriage to mystery man number two and her children were during the same time she was married to my relative and had her daughter, also my relative. So I went to the source. Wrong. I never wrote down a source. Not in my program which has a definite source section, not on any scrap of paper I could find. So now I cried, not because I couldn’t find the source, but at the thought that in my official family tree there was an error.
I knew I couldn’t be wrong, I just couldn’t, but now I had to prove I was correct by not only finding the original source but proving it. This took away all my free time over two days. Had I written down the source the first time. I would have saved at least a day and a half. Once I found my original source, it proved absolutely nothing, except that maybe I just copied someone else’s tree without verifying it. This could be because my original source was the online family tree of a far flung relative. Now I had to prove it.
Proving it required searching every spelling of her last name I could think of and every spelling of her potential parents in a foreign website who’s records at any given time can be in three different languages (French, Latin or Dutch or even local variations of Dutch). Once I found the index I had to search page by page for the actual birth record to prove her parents where her’s and find her marriage record to prove my ancestor was indeed mine and married to the correct man. I now have a printed copy of her records and have noted my source and when I have some time I will go back a generation. Her mother’s mother seems to have 5 different spellings of her last name. Actually 5 different last names because each spelling sends you in a unique direction.
Sources, they save you valuable time, energy, and doubt. It’s a simple thing to write down for yourself.