[Stanfoo]

Is it bad if I set the gain on in the E09K? People recommend to turn it off, but I need the extra sound. What negatives from doing this?

 

[SteveHiFi]

I'm not sure of the context in which it was suggested the gain be left down - maybe for low impedance headphones or IEMs?
 
If you need the juice, use that gain switch - I can't see any problem.

 

[mindbomb]

  Is it bad if I set the gain on in the E09K? People recommend to turn it off, but I need the extra sound. What negatives from doing this?

what people are saying is that if you had the choice, low gain and a higher setting on the volume dial is better than high gain and a lower setting on the volume dial. If you can't get enough volume with low gain, you can use high gain - that's why it's there.