Nothing. You can smoke for days applying good blue smoke and never over smoke. You can smoke for 1 hour and over smoke. Then you can create beautiful smoke and just over power the meat for those intended. Its a balancing act.
First you must realize what those you are smoking to feed will appreciate most. Some want huge mesquite , others want a lighter fruit smoke. Know your crowd, never hard smoke meats for folks you'll feed the first time. Smoke is an acquired taste.
Thin blue smoke is aroma. It embeds that smell that just drives folks wild for "BBQ" when they really are thinking smoked. Its enhances the perfection of the properly cooked food.
Too much smoke gives an acrid or bitter taste, you'll know it when you taste it. Its normally caused by too much smoke too fast. Its a rookie mistake and the reason everyone knows that taste, is thru there own experience. LOL Normally when you expect to see too much smoke is when the clouds of billowy white clouds come continuously chugging out the stack. Its not really too much smoke, its too much too fast.
My humble opinion.