OSX defrags itself during regular operation. Some systems that have been running and changing files often for 4 years can encounter an issue ... people try to create a BootCamp partition after 4 years but the space cannot me "moved" at the end of the disk partition. If you simply clone the partition (copies contents, not the "location" of the files) and re-clone-back, it will be clustered again at the beginning.
But most system users will never see this issue unless (A) files become "fixed" after years and (B) people BootCamp.
Do we need to use system tools like a PC would- if so what???
No, 99% of most users don't need to do anything to maintain a Mac.
However some do, if the Mac has a hard drive and it's slow, some steps can be taken to speed it up.
If you want to clean the Mac of hidden stuff, like caches etc. then CCleaner for Mac and OnyX for OS X will do the trick, followed by a Security Erase (Zero) of Free Space using Disk Utility. (if a hard drive)
OS X has never required disk defragmentation: http://support.apple.com/kb/HT1375
I've been using Macs for 27 years, have never defragmented or used OnyX either. For that matter, I have never used any optimizers, "cleaners", "accelerators", "scanners" or any commercial anti-virus junk.
Other than a router, I have no firewall, and I have never had any malware problems.
I keep my systems updated with Software Update or the App Store, and I use Time Machine in case a hard disk fails (none ever have though).
What I don't do is click on unknown links in an email, download torrents, or volunteer my account name and password unless I know what is requesting it and why.