Ok, your open tuning is E - A - D - G - B - e. (all strings strummed open)
If you tune down 1/2 step the open tuning would be Eb - Ab - Db - Gb - Bb - eb. (all strings strummed open) Say the key to this song is "Gb". Your chord progression would be Gb - B - Db. (this is if you were playing in open E tuning) These are difficult chords to make so by tuning down 1/2 step you can play tour simple open G - C - D chords and the voicing will be correct.
So get your guitar and tune down 1/2 step for the songs where you need this tuning. Now you have just played your songs with this tuning and want to play something that is in a typical open E tuning. Instead of having another guitar standing by in open E tuning and having to swap in order to play your next song you would simply place your capo on the 1st fret and you would be back to E - A - D - G - B - e and could play all your bacsic chords without any problems.
A capo can be your best friend once you learn to use it. Some people call it a "cheater" but it is a good tool to have. As a quick lesson, you are playing in open E tuning (E - A - D - G - B - e) in the key of "G" (the chord progression is G - C - D). The next song called out is in the key of "A"
(that chord progression A - D - E) You can put your capo on the 2nd fret, play your G - C - D chords and the voicing will be A - D - E. Move the capo to the 4th fret, play your G - C - D chords and you will be playing in the chord progression for the key of "B". Capo placed on the 5th fret and the G - C - D chords and you will be playing the chord progression for the key of "C".
Learn your notes on the fret board. Learn the root notes to your chords. Learn to transpose the key of a song.
Hope I have not confused this issue.