The only effect I can think of is that it may be a bit more hoppy than you planned. What I mean is, say it was a 1.054 brown ale with IBUs of 26.5. If your efficiency was poor, you might have a 1.044 brown ale with IBUs of 30. That's not even a noticeable difference, but it might be more noticeable in a bigger beer.
Otherwise, aside from a slightly lower ABV, I don't see any problem at all with a lower SG beer.