Several years ago I worked through a set of DNA matches and reached a conclusion about the paternal grandmother of the testee. I felt strongly that my reasoning and conclusion were correct. As more matches have come in for this test, they have all been consistent with that original conclusion.
That’s not the problem.
I never wrote up my analysis and recently a correspondent, new to genealogy and from a different part of the family, asked me about the testee’s relationship to the paternal grandmother. The correspondent very nicely asked me “how I reached my conclusion.” She wasn’t doubting it, she just wanted to know how–partly so she could see if my conclusion was correct and also I think to help her with another part of her own family.
It took me half a day to go back through the results, re-create the analysis, and write it up. It did not hurt me to do it (and could have helped me catch an analytical mistake), but it wasted time that I could have been doing something else.
Whenever any conclusion requires time and analysis to reach: write it out then. You’ll be glad you did later.