With all due respect to John Huber, who is a seasoned Forum contributor, I have a different opinion about this. I have no technical or progamming background but am an experienced longtime Mac user. DiskUtility (formerly Disk FirstAid) is an important tool for checking & repairs. It serves as a first line utility for dealing with disk or OS problems.
However, my experience has been that it detects only some types of problems . There are various third party products designed to address this area also: Norton System Utilities, TechTool Pro, Disk Warrior, and others. Each was designed to address specific types or ranges of problems. While there is a bit of overlap in types of tests they perform, each package has some unique features it addresses while not addressing others. Each product has its own strengths and weaknesses. There are some Mac users who will swear by one product and berate another.
I have found that the third party utilities I have used would frequently pick-up minor or latent errors even when DiskUtility reported no errors. My own experience is that no one of them was "the best" or could address all problems. One program could fix some the other did not. Consequently, my opinion and practice was to have more than one I could use. I considered the cost as good maintenance and insurance. I did not NEED them often but when I did ... they helped my repair or recover from situations that could have led to data loss (as well as major loss of time).
With regards to your specific question about Disk Warrior, I do own and use it. Compared to other utilities, DW focuses more narrowly on the disk's catalog & directory structures. And it does a very good job with this.
With Symantec dropping its support of Norton DiskDoctor or SystemWorks, the remaining choices for more comprehensive utilities are TechTool or Drive Genius -- both available thru Apple Stores.
Needless to say, don't overlook or forget the important related lesson to this ...... regularly make and safely store backups of our important data.
