I use the “wait for full load” option at first stop when I begin running a line. You can then buy many vehicles and leave them to it while you do other things. When they are spread out I turn that off and let them run as fasst as they can cause I discovered that often the site that turns raw material into goods somehow start to produce more goods then incoming raw material. You discover that when those packets start walking themselves along the road from that site. Then you have to pull out all stops and buy more vehicles to catch up.
So we have
1) stop check for cargo but drive immediately
2) wait for full load
why don’t we have
3) half full
4) 75% full
5) or just be able to set the percentage yourself
or
6) decide what cargo you want to carry like 50% raw materials and 50% refined goods.