Under little endian, the same power digits of differently sized operands are at the same offsets. For instance, whether we have a 16 bit operand or 128 bit operand, the least signficant 8 bits of either one are at the lowest address and so on. This is important if we want to, say, add them together.

However, this effect can hide bugs under little endian, which will instantly reproduce on big endian.

Suppose that, say, a function expects a 32 bit parameter, but the caller thinks it is passing a byte, whose value is XX. Suppose that by fluke the memory is all zeros. Under little endian, the caller puts XX at the right memory location in the stack, resulting in XX 00 00 00. And, by golly, the callee gets the corect 32 bit value XX.

Under big endian, even if by fluke the memory is all zeros, the caller will put the XX byte resulting in the same XX 00 00 00. But this now looks like a huge 32 bit value to the callee, hopefully caught in testing.

The apparently correct value will not be caught in testing.

Little endian would need nonzero values in the extra bytes instead of the fluky zeros in order to see a bad value.