Personally, I like the method used by Taylor in their string-changing video. But I gotta know... Why leave the strings untrimmed for a couple days?
So you can scratch the heck up out of your headstock, LOL, Just Kidding.
Stu, I am sure everyone has their own way to change strings and as long as you get the end result of the guitar staying in tune without damaging it in a any way before or after the string change then I consider it a success.
I used to lock the string ends in between winds on my guitars when doing a string change as this allowed for the quickest return to tune with the minimal amount of slippage. In other words if I broke a string on stage I could put a replacement on and after tuning it up to pitch I didn't have to worry about it dropping in pitch right after changing it because the end was clamped between the winds themselves. This allowed you to get right back into playing live with minimal adjustments.
These days I prefer to get at least 3 wraps around each tuner and instead of clamping the strings between the winds. I prefer to use the natural friction to hold them in place. The way I measure how long to cut the strings is very easy. Once you have inserted the string into the bridge with the bridge pin and are certain that the ball end is seated properly against the inner Bridge plate you stretch the string up to the post it is going on. Then you mark the string one post higher than the post it is going on and cut it there. For instance, If you are replacing the Low "E" string you would extend the length to even with the center of the "A" string post and cut it there. If you were installing the "A" string you would extend the length to even with the "D" post and cut it there. If doing the "D" string which is the top post, you would imagine a post above it the same distance as between the others and cut it there. Back to the low "E" string, Once it is cut to length you can take a pair of Needle nose pliers and bend approximately an 1/8"- 1/4" of the end of the string Away from the headstock out to the side. Then hook that end into the post and start winding tension on it making sure that the winds are going below the the end you hooked into the post. Keep tension on it while winding it and eventually the natural friction will take over. Go ahead and tune it to pitch and start on the next one.
NOTE: On a 12 string I measure and cut the string length to the center of the second post up from where the string will go. This is for 12 string guitars only.
For me this makes a very clean headstock area with no string ends to scratch your headstock face and no short string ends to catch and tear your cleaning cloths. Also if you have to remove the strings for any reason before their lifetime is up and wish to re-use them it is extremely simple to just slide the winds back over the post and hook your bend once again. Then re-tighten them ad you are right back to playing. This is extremely economical as some string sets can cost upwards of $25-$30 a set. Sometimes removing them before they are worn out to perform maintenance on the saddle, string nut, or frets can cost you a set of strings. With this method you can reinstall the ones that were on it and still in good shape without wasting them.
I hoe this helps and doesn't confuse anyone, Once you get the hang of it you can be pretty quick about changing the strings. I can change a set of 6 strings in about 10 minutes with one bad arm including cleaning the fretboard all while the guitar is upright on the stand. 12 string sets take me a little longer but no more than 30 minutes even if I a just relaxing while doing it.