Dropping your guitar's tuning by half step, as so many rock guitarist do, is just to accomodate the vocal range of the lead singer in the band. It serves a double purpose as it also accomodates the guitar player, it means that the guitarist can still play easy open chords with this drop tuning in stead of having to play more challancing bar chords in standard tuning in order to drop the key of the song by a half step.
Anyways, with equal temprement, any song can be transposed into any key you see fit, and the song will still sound perfectly good. A song written in the key of A with a progression like A-E-D can be transposed to be in the key of Ab, a half step down, so the progression would now be Ab, Eb, Db. If you play both progressions, the song would sound exactly the same, except the second song will be a half step lower in overall sound.
Instead of having to stuff around between standard and dropped half step tuning when learning songs, keep your guitar in standard. Whether your keep your guitar in standard or tuned half step down, it would not matter and won't change anything in the song. The only time there will be noticable difference if is when you want to play along with the original recording as all chords and notes will be a half step higher or lower on your guitar.
Anyways, the choice between having a guitar tuned to standard or half step down should be based on the singing. If your vocal range (of someone else doing the singing) can accomodate you to sing better along with Ab-Eb-Db, instead of A-E-D, keep your guitar tuned half step down. It just makes sense playing easy open chords like A, E and D with a guitar tuned half step down than playing Ab, Eb and Db on a standard tuned guitar
Just a note, it is just easier to have two guitars, one tuned standard and one tuned down half a step