Hello @Patrick,
The product length has been introduced because some shipping module takes the length (ups, postcanada, boxtal, fedex ..)
You can define different length in function your need.
When you create a new shipping app, you can convert the length in function of characteristics of the service. For example, in France, we use the cm but in USA, this is the inch. If you have your length in cm, you can convert automatically in inch .
Some others updates resolve bug fix.