There is an additional reason for not running lean, which applies very well to turbocharged engines - the extra fuel creates a 'boundary layer' between the combustion products and the cylinder wall. This absorbs extra heat during combustion to help keep the chamber temperature within tolerance. Modded cars that run very high turbo/supercharger boost are frequently on the point of running too lean, in that the injectors cannot supply sufficient fuel to maintain this boundary layer, and the combustion chamber pressure/temperature increases. In extreme cases this results in detonation/knocking, and under high boost can cause physical piston damage.

There is an additional reason for not running lean, which applies very well to turbocharged engines - the extra fuel creates a 'boundary layer' between the combustion products and the cylinder wall. This absorbs extra heat during combustion to help keep the chamber temperature within tolerance. 

Modded cars that run very high turbo/supercharger boost are frequently on the point of running too lean, in that the injectors cannot supply sufficient fuel to maintain this boundary layer, and the combustion chamber pressure/temperature increases. In extreme cases this results in detonation/knocking, and under high boost can cause physical piston damage.