Do Mac disks need to be defragmented?
If you are defragging Mac hard drive just to increase its performance, then you can resolve these issues very efficiently by the help of below mentioned free tips: -

1.Quit all the open apps to free up some memory. Many times, they become the primary cause of system slowdowns. 

2.Reboot your Mac system. It will clear all the caches, free up memory and also allows the user to install any necessary core updates

3.Updates your Mac OS X to the latest version to perform better than the previous version and updating OS X will fix certain bugs

4.Try to make sure that you have at least of 10-15 % of your total hard drive is available at that time to adequate proper cache and other temp files

5.You also need to check for a failing drive using the help of Disk Utility. If the drive is failing and won’t repair, then you need to fix it using the help of proper methods like the one mentioned here.

Older version of OS X needs to be defragged, if necessary. You may consider one such application mentioned here. However, Mac OS Yosemite and its later version don’t need defragmentation.