Compatibility is an indication that a product meets some or all of the specifications for a particular standard. For example, if a program is IBM compatible, it can run on any Dell, IBM, Hewlett Packard, or other computer with that same set of Windows-compliant components. Apple computers that utilize the macOS X operating systems are not IBM compatible.
Although macOS is not IBM compatible, Bootcamp can be installed that will allow it to run many IBM compatible programs.
If hardware is incompatible with your computer, but can still be connected to the computer it may damage the computer. However, it is most likely the computer will not work until the incompatible hardware is removed. For example, if you instal memory into your motherboard that is incompatible your computer would not boot or get an error as it is starting.
Computer software that is incompatible with a computer (does not meet the system requirements) will be unable to run on a computer or get errors and run slow.