I don't see the double negative that Paulster 2 seems to read.
"In a synchronized box, it is unnecessary to shift without a clutch."
That is a true statement. I don't think it could be any clearer. Some drivers, especially those driving large and heavy trucks, feel like they're saving time and shifting quicker if they float gears. Most of them are driving trucks that aren't theirs, so they have no stake in treating it kindly. Terrible attitude, but that's the way it is these days. I'm old school, and I was taught to take care of that which is not mine simply because it's not mine.. They seem to forget that the big rig they're thrashing the gearbox in is a tool to get two jobs done; one, to move freight, and the other to make a living. If the truck goes down for a transmission failure, no freight gets moved and the driver with the bad habit gets no pay. Some drivers think clutches are for sissies. This is twenty years and almost two million miles of hauling fresh produce across the country and another twenty years of working on man-rated space hardware (specifically proof testing almost every part of the Space Shuttle Main Engines) talking. I'm so glad I never learned how to float gears.
If the shift is well-coordinated, that is, timed well, using the clutch will create a seamless, smooth gear change that can outperform any automatic transmission. One has to listen to the feedback the truck is giving. The trick is to learn what the drivetrain wants and then give it. Too many drivers fight the truck and try to beat it into submission. That's like beating the donkey because you overloaded the cart. The transmission will tell you when the timing is right, just like it'll tell you when you're wrong. It's a rhythm, and with or without the clutch the gear change can't be made unless everything is rotationally ready. The purpose of the clutch is to assist in achieving synchronization of the rotating parts and greatly reducing wear. The operator still has to learn the correct timing of the gear change, upshift or downshift. Once that is achieved, therein lies the pride and satisfaction of a job well done, without any wear on the gearbox or clutch or any other drivetrain part.
Use the clutch, Luke.