Someone once said to me that if you need to read the words at a gig you'll never learn them and there's some truth in that. A friend of mine sang a well-known song (with only two verses) every week for well over 10 years and couldn't do it without the lyric sheet in front of him.
'In the old days' we wrote the lyrics out manually and this probably helped you absorb them to some extent. In these days of 'cut and paste' that benefit has gone.
I must hold my hand up and say, as I get older my memory doesn't seem to work as good as it did, especially when trying to learn new songs, so I do like to have the lyrics close at hand for those embarrassing CRAFT moments.