I use a capo a lot because I play with a band that does the Dances of Universal Peace songs. These were developed for voice, guitar, recorder, and percussion. Most of the songs are modal ... a few have extra notes. But few of the songs are in D ionian or mixolydian or B minor, the modes easily played on a DAA or DAD tuned dulcimer. In fact the most common mode is C minor, with D minor fairly common as well, and songs in C ionian/mixolydian, G ionian, and so forth. I ended up adding all the frets to one of my dulcimers so it is fully chromatic, tuning it to CGG so I can play all the notes of any of the songs on the melody string, and using the capo to play songs in many of the key-mode combinations such as D minor. I have a second dulcimer tuned either DAA or DAD for the songs in D ionian or mixolydian, and capo in the DAD tuning for the tunes in G and A ionian and a few others that fit. This provides me with maximum flexibility as we move from song to song and allows me to play every song in the repertoire with two dulcimers and at most tuning one string on the DAD/DAA dulcimer if needed. I find that if I mash too hard on the capo while I'm tightening the screw, the strings go out of tune - as a previous comment noted. Also they seem more prone to this if I have the capo right next to the fret. So I place the capo a bit to the left of the chosen fret and hold it down some but not too much as I tighten the screw. I check for proper fit with a quick strum or two. After doing this several times on each dulcimer I developed a good feel for the placement and amount of mashing to do. I encourage use of the capo. Like tuning and playing in different keys and modes, it takes practice and getting used to. The reward is the ability to play a much wider variety of songs.