Not a problem if it happens only once in a while. The following is a reproduction of a simple explanation.
"Your emission control system actualy consists of several sub-systems, one of which is designed to prevent raw gasoline vapors from being released into the atmosphere. It does this by trapping the vapors in a charcoal-filled canister so they can be drawn into the engine and burned later when the engine is running. If you continue filling the tank beyond the normal "click-off" point you can overload the system with vapors. This can cause the engine to run "too rich" and could eventually ruin the charcoal canister."
'93 300E 4Matic
'98 Nissan Altima
'00 Yamaha Road Star Silverado