Should I update the corresponding class when run tunetable?

Online document says: TUNE TABLE updates the SQL table definition (and therefore requires privileges to alter the table definition). Commonly, TUNE TABLE also updates the corresponding persistent class definition. This allows the gathered statistics to be used by the query optimizer without requiring a class compilation.

I don't get the point. If I run tune table once with  class update and next time no class update,  does this cause inconsistce of sql definition and class definition? What happen if I recompile the class ? will table stats in class definition will overwrite which in the sql definition? 

then, what this the usage of class update with tune table,  for exported the class definition with table statistics in this instance ? 

thank you for your time