Back in the day (and even now with the big rigs), automotive transmissions didn't have synchros. If you don't know what a synchro is, it's the part of the transmission that matches the input shaft speed to the driveshaft. If you've ever jammed your stick into gear too fast, or into the wrong gear with too much force (even with the clutch pressed) and grinded it a little, that was because you didn't give the synchro time to spin up to the right speed. Anyway, before synchros, the best way to shift quickly was to press the clutch, move the stick into neutral, let out the clutch (this would engage the input shaft to spin at the right speed), press the clutch again (hence, the name), and then put the transmission into your desired gear. Like PMAZ said, it's not much of an issue and unless you're a professional driver; not worth the training to get it right.