Too Long; Didn't Read
Mach-O is a binary stream of bytes grouped into meaningful chunks of data. These chunks contain information about the meta like byte order, CPU type, size of the chunk and so on. The starting memory address is randomised every time your app launches using a nifty technique called Automatic Space Layout Randomisation or as we lovingly call it ASLR. This is done for security purposes, otherwise, it would become very easy to hack the binary if everything has the same address on every launch!