Hello,
There are many utilities that cause far more problems than they help. Some can corrupt your data, some can slow your Mac to a crawl, some are even malware disguised as a utility app.
-There are several third-party utilities and software that one should totally stay away from: MacKeeper, MacCleaner, many Norton utilities, many antivirus apps.
-There are some that are borderline, seem to be OK, but I don't normally recommend them: CleanMyMac, Carbonite, Dropbox, etc. CleanMyMac seems to have been updated to be a useful app these days, from what I have read recently.
-There are many that are recommended highly: DiskWarrior, Drive Genius, TechTool Pro, Malwarebytes Anti-Malware for Mac, OnyX, Cocktail, ClamXAV, etc.
I don't recommend running antivirus apps with real-time or on-access scanning enabled. I also don't like background monitoring processes like TechTool Pro's eDrive, Drive Genius BootWell/DrivePulse, etc. I actually install all my utilities on an external HD, so I can diagnose/troubleshoot/perform maintenance when it is convenient, and manually as I see fit. I can also use them on multiple Macs that way.
Also, I am not a big fan of Adobe and Microsoft software any longer, as they have become very bloated and annual subscription based. Adobe Flash is one of the worst offenders of all, second to MacKeeper. If you need Flash capability, I recommend you run Google Chrome and enable its built-in, sandboxed version of Flash.
There are others, so feel free to ask us our thoughts before you try/purchase.
Hope that helps,
C