It's a useful attribute, just as priority, to evaluate task priorities.
In our case, we need to be able to sort for that field.
When you have to evaluate which task has more weight to go first, and maybe all has the same priority. Maybe you could use weight as an indicator of resources, hours, user interested (as you do here with canny).
Custom fields are not uselful in this case, because to see the value, you need to open the task, and you cannot sort for that field.
Thanks in advance!