For weapons with an average damage of 15 that 5% boost should give you 1 more shown in your stat sheet window. Equates to 3 more per hit when doing max damage AIs (like with a specific slayer).
Against, something with ~10k HP, you'll hit it ~3 or 4 fewer times...
In PvP, since what you're hitting will most likely have 75 resist, and you're capped at 35 dmg on an AI, you might get it to round out that you do 1 more avg damage per swing.
Probably not worth the effort of dealing with, if you've got some other mod you'd. You'd probably find that having 4 more HP (like imbue 8 str on a jewel instead of 15 anat) more useful than doing 3 more damage per hit.