I play with a bunch of old time musicans. If you take away their capo they could not play. They mostly play 3 chord songs with maby a minor chord or 7 chord trown in. Just by knowing a few progressions, having a capo available and they are set. Take the chord progression of G...C...D - typical open chords, right? Ok, capo 2nd fret and play G...C...C - chord voicing is A...D...E. Hmm, capo on 3rd fret and play G...C...D - chord voiceing is Bb...Eb...F. Moving up to the 5th fret with the capo and play G...C...D - chord voiceing is C...F...G.
Pick a chord progression - say C...F...G. Capo on 2nd fret and play C...F...G - chord voiceing is D...G...A. Go to the 5th fret and place the capo - play C...F...G - the chord voiceing is F...Bb...C.
Thats the beauty the capo. If you know just a few open chord progressions, understand where the capo needs to be to achieve the key you need there are 1000's of songs that have now become easy.
I have a very good - easy to read and understand - capo conversion chart that I will gladly send to someone in an e-mail if they will help post it to this forum. Just let me know