Once the essentials, such as medicine and key business documents, have been accounted for, it is wise to err on the side of underpacking.
The amount of stuff that is carted from one destination to another and back while being used for nothing other than burning fuel, taking space, and creating guilt feelings on the part of the bearer can be sizable. It is huge when multiplied by the total number of travelers.
If brutally honest with ourselves, we would designate an extra bag solely for the things we won't need but somehow feel compelled to take. If wise, we'll "forget" to take that one.