[airtractorfan]

Playing songs from a church hymnal with a piano player is a very good reason to tune down 1/2 step to Eb. Most songs in the hymnal are written in flats[a few in sharps#] which allows a guitar player tuned to Eb to play on the dots[fret markers] instead of between the dots.A song in Eb allows you to use the 1st position E chord and open string notes also.
Most church piano players had rather play in flats instead of sharps.Most of the Keys that we guitar players use are sharps# [ A G D E ] Please reference the Circle of Fifths.

Example : Amazing Grace in a church hymnal is usually written with 1 # next to the treble cleft which is the key of G
A lot more of the songs are written with b[F] bb[Bb] bbb[Eb] bbbb[Ab] bbbbb[ Db] flats next to the treble cleft than with sharps#.

I was at a Bill Gather Homecoming Concert and Bill told the new piano player who was blind to play a particular song in 4 flats instead of using the letter Key Ab. As a guitar player I would much rather play tuned down to Eb and play in the 5th fret position on the marker than standard tuned on the 4th fret position with no dot.

I do agree that a guitar player should know the fretboard well enough to play any song in any key [standard or Eb tuning] without the use of markers but I'm all for doing it easier.