Would an accurate weight of a loaded aircraft be helpful?
A friend of mine was FO on a regional jet with 50 passengers. During the take-off, the PIC could not rotate the plane at the calculated VR, but only much later. They reported the incident during the flight. The luggage containers were re-weighted at the destination, and it turned out that one of the containers had a grossly wrong weight recorded at the origin. 

Weighing mistakes can end in a disaster, especially for smaller jets. Systematic weighing of ready to launch planes would eliminate this risk. I am not aware of an accident caused by this kind of weighing mistake, but surely there have been accidents due to overloading or wrong load distribution.

The technology to build load sensors into the undercarriage is available and it appears that a few planes are equipped with it. 

On the other hand side there must always be a risk assessment with a trade-off between costs, likelihood and severity.