Logging the same thing every day can be tedious. Some things that are logged change less often and stay the same more often. In these cases, it would be nice to assume that the metric in question takes on a particular value for the day, rather than zero/no if that metric is missing.

For example, if someone always has one cup of coffee per day, it could be more convenient to simply assume they drank one cup, and let the user change this value to something else if they deviated from that. The default value would appear when the user views the form