I use a stand when playing in sessions because the range of music isn't all "mine," but "ours." But for songs I sing alone, I never feel emotionally with them, the good ones, until I can sing them easily "by heart"-- a very descriptive phrase, if you ask me.

It is also surprising to me that using song sheets, even for months, I don't learn the song...still have to refer to wordsm chords. Seems, for me, there is no other way than slogging thru memorization.