The legitimacy of using tablature in teaching the guitar has been a hot issue for a long time. Some think it is a way to make learning easier and quicker while others consider it a crutch or even a cheat. One thing is certain: the nature of the guitar is so unique that this issue would never apply to any other type of instrument.
Conventional music notation was actually derived from vocal music notation of the Middle Ages. Thumb through a music history textbook and you'll see pictures of Medeival scores with 7 and 8-line staves, funny shaped notes, runes and the like. These were to be read by singers in solo or ensemble settings. The human voice is a 'monolinear' monophonic instrument, making the choice a simple one. There's only one place to sing a high C. A similar situation exists for nearly all wind instruments and even many polyphonic instruments, especially keyboards.
The additional challenge posed to the sight reading guitarist is obvious. The guitarist has to make certain instantaneous decisions and then choose a position and fingering that will make the notes most easily playable
The guitar, however, is a 'multilinear' instrument. This adds a layer of complexity to the process. Having to choose where to play a particular pitch is not the exception but the rule. In fact, one can play the same scale (identical pitches) in any one of a dozen locations, positions and fingerings on the guitar fretboard.
The additional challenge posed to the sight reading guitarist is obvious. Sitting in front of a piece of music, the guitarist has to make certain instantaneous decisions that other instrumentalists will never be faced with. Upon seeing a grouping of notes, the guitarist has to determine the pitches and rhythms (like everyone else) and then choose a position and fingering that will make the notes most easily playable (something almost no one else has to do).
Certainly there are exceptions to this. One that comes to mind is the F attachment on a trombone, which changes the length of tubing at the flick of a switch, giving the player additional choices as to where to play a given pitch. But I stress this is the exception, and was designed to make trombone playing easier.
So what does all this have to do with tablature? Look at these examples of lute tablature:
Here we see lines representing strings on the lute and not note heads but alphanumeric characters, indicating what fret should be fingered. With this system, it's much easier to visualize where to play a given pitch. In fact it's quite specific, streamlining the process and making sight reading an easier task. Many guitarists feel this kind of notation is far more logical for guitars (and other fretted instruments) than the one we have today. Looking at these examples, it's difficult to argue the point.