Isn't it obvious? More code to skim, scroll over and maintain if something changes. If you add a struct field, your manual EQ implementation still compiles and seems to work but is wrong and will lead to bugs. Yes, solving this for 99,999% of cases with an attribute is just far superior and does make a difference (while keeping it easy to manually implement it if needed). Hash and Ord and some other traits can be implemented in a similar fashion btw..