Computer architecture why is MemRead used?
Wouldn't having MemRead always enabled just cause Read Data to always output whatever is currently stored at targeted address


Yes, it would output whatever is stored at the targeted address, but the targeted address might be from the last write operation.


  or ignored if not required via the multiplexer


If the multiplexer is set to 0, the address will be output. If you want to hold the read value constant while write operations are happening, you would need to set MemRead low, and the mux selector, MemtoReg high.