Cutting in front of trucks approaching traffic lights reduces the safety margin allowed by the truck driver to give ample room to stop and to possibly still be moving when they change. If you fill this space, you risk damage from behind.
A loaded B-double can weigh up to 50 times that of your average car, and it is not physically possible to stop instantly. Some people do not seem to be aware of the energy required to move up to 64 tonnes of B-double off from a standing start and conversely the distance needed to stop one.
Drivers of all large vehicles try to utilise the rolling momentum as much as possible by flowing with the traffic and holding back at lights to be still moving when they change to green.
You will not save any time on your trip if hit from behind by a truck because you filled the space that the driver allowed to slow.