Did you do any thinking to reach that genealogical conclusion about a parentage or a date? Did you analyze several documents to reach a decision about what they meant? If so, is that chain of thought somewhere in your database? Human memories are particularly frail and writing it out somewhere increases the chance your logic and thought process gets preserved.
And remember that you could later realize you were wrong. It is hard to see an error in your line of thought if it was never written down anywhere.