Well, machines usually needs to have the particular type of RAM they were designed for. For some, it would be DDR SDRAM memory, for others, DDR2 or even DDR3 SDRAM memory. Or pre-DDR SDRAM memory for older machines.
It's all about whatever memory the machine was designed for. No particular advantage in mismatching the wrong type of memory to the machine and usually involves a lot of grief if done that way.