About checking the MD5 of Ubuntu iso

Is it possible that my iso file is not 100% matching the download, but Ubuntu will still let me install, and I will actually have a working Ubuntu but that is working with lower performance than expected?
(Assuming I didn't check Md5 before installation), Or it can't be, and if I managed to install it, it means it installed as it should?

I always have a thought that I might install something with some broken files in it, but they're not seen so I won't be able to tell

Thanks!