march=native turns on all the features for that are available for your processor. So if, for example, you have a processor that supports AVX512 and another that

march=native turns on all the features for that are available for your processor. So if, for example, you have a processor that supports AVX512 and another that doesn't, you'll get illegal instruction errors as soon as your other machine hits a region code it decided to optimize using those instructions. You won't get any real useful error messages when this happens since it's so low level. Unless you know to look for this you'll just be scratching your head going, "but it works on my machine?!?"