I found a good explanation of why franklin would recommend cleaning wood joints before gluing them....
https://content.ces.ncsu.edu/wood-surface-inactivation-and-adhesive-bonding
In this case, the article recommends gluing shortly after machining if possible. The suggestion to sand joints probably seems like it's to make a rough surface for glue to grab, but might have more to do with making a fresh surface that hasn't "aged" and had a bunch of ambient stuff microscopically make residence with possible binding sites.
https://content.ces.ncsu.edu/wood-surface-inactivation-and-adhesive-bonding
In this case, the article recommends gluing shortly after machining if possible. The suggestion to sand joints probably seems like it's to make a rough surface for glue to grab, but might have more to do with making a fresh surface that hasn't "aged" and had a bunch of ambient stuff microscopically make residence with possible binding sites.
