It's a good idea in languages that are both a: statically typed (so a variable that can contain 0 is not also able to contain False) and b: weakly typed (so int

It's a good idea in languages that are both a: statically typed (so a variable that can contain 0 is not also able to contain False) and b: weakly typed (so integers can be implicitly treated as boolean at all). Whether it's a good idea for a language to have both those properties is debatable, but if "if(statically_a_int)" is valid at all, "is zero" is one of the only sensible interpretations ("is negative" being the other, but that doesn't generalize to unsigned types well).