Question: In a song I am learning, there is a section of the song that has the chord progression G#m | A#m7b5 | B6
I sometimes get the fingerings wrong and use dimished 7th chords on guitar instead of m7b5 chords and in this case I actually think the dimished7th chord sounds good too. So I wanted to ask, what is the difference functionally between the two? They both seem to work in most situations as leading tone chords to a tonic chord one semitone above (B in this case).

Answer: 
While m7♭5 chords and dim7 chords are fairly interchangeable as dominant-function chords (don't interchange them if the melody note is the 7th), the dim7 chord is a much better **pivot chord** between keys than the m7♭5 chord, as any given dim7 chord is an enharmonic re-spelling of 3 other dim7 chords, while a m7♭5 chord cannot be enharmonically re-spelled into any other m7♭5 chords. When a dim7 chord is acting as a pivot chord, interchanging it is unwise.
Do m7ba and Do dim7 are exactly the same chord:

```
Do m7b5 = Do dim7
 Do (root)
 Mib (minor third)
 Solb (flat fifth)
 Sib (seventh)

La# m7b5 =  La# dim7
 La# (root)
 Do (minor third)
 Mi (flat fifth) (perfect fifth would be Mi#)
 Sol# (seventh) (mjor seventh would be Sol##)

```

Anyway, it sounds weird to call A# dim7 and Gm#, are you sure it wouldn't be Abm and Bb dim7 instead?

What geometry for both chords are you using on guitar?