DoL but actually the effect I've seen is to increase the number of attempts per node. I guess that effectively increases yields but its more desirable to get extra attempts per node because that is extra SP and less time running around.
I'm not sure what the thresholds are but you could potentially get more than 1 extra attempt with more output. The difference is especially significant when you're on the border of making a switch to the next tier. With no output you might only be getting 2-3 attempts per node and with output you might get 4 or even 5. With those attempt numbers plus getting 110+ SP per hit, that is quite an increase in SP per hour when you're mining/logging.
Wada: "There may be some areas of testing that were lacking or too rigid."