Not the best shot in the world, but this is what I did to run power straight off the battery:

 

Both are very clean looking and well done. I think for "lower" wattage applications like 500 or less....you are probably not going to have an issue doing either. I think that if you went significantly higher then that you may have a charging issue by not doing the battery directly off the terminal.
This really also depends on how good the amp is, the install is, and the quality of the wire used.

 

final decision has been to run directly off the battery just to be safe as I am running a 1000watt amp and don't feel like changing it if there are any issues. Wish me luck, I'll be doing the install on monday.