A good - and importantly, trustworthy - disk utility is always a must-have in a user's toolkit, whether power user or otherwise. In the Windows world I have long relied on WinDirStat to troubleshoot systems where the disk is imminently about to run out of space, and I have used Piriform's CCleaner to purge junk files and reclaim space.
Yet, I have never had much success in finding a good general purpose, "go to" app for disk maintenance on OS X. I was excited when Piriform released CCleaner for MacOS but it is only a shadow of the Windows version. I tried Disk Inventory X and while useful to a degree in finding large files, it wasn't quite up there in terms of must-have utilities.
Disk Xray performs three fundamental functions, and it performs them well, with a simple and consistent interface that does just what you want in a minimum of clicks.
The first feature is to scan folders - be it an entire hard disk or a subfolder - giving a sorted breakup of just where your disk space is going. At a glance you can identify which folders are the space hogs and just what is in them by successively drilling down. The scan operates quickly and options allow you to select only specific types of files - such as music - and to include or exclude package contents and invisible/hidden items.
This feature in itself justifies the app; if your disk is filling up you can within mere seconds determine the biggest contributors - or offenders, as the case may be - such as large videos, rogue log files, or something else.
You can choose a folder or hard disk as your starting point, restrict by minimum file size, and include or exclude hidden items and system folders.
Both the folder scanner and duplicate detector allow you to open the Finder at the location of any specific file or folder so you can perform your own inspection.
The third feature of Disk Xray is a disk cleaner, scanning your user folder for items that you could possibly delete to save room. This includes the obvious choices of the trash and your downloads folder, and also includes locations you may not otherwise think to purge or even know where to find - application logs, web browser caches and cookies, application caches and an ever-growing list of email attachments stored locally but never cleaned.
By careful use of the Disk Cleaner tool you can remove files that are no longer relevant or necessary, further tidying your hard disk. You can move items to the trash from within the app, with a menu option giving the safeguard of undoing this action if you make a mistake. As with the other two modes of Disk Xray you can open the folder at the location of any item to perform your own inspection and investigation.
Disk Xray is available on the Mac app store for $8.99. You can also buy it through the vendor's web site, as well as download a 14-day free trial, or purchase a group license for organisations with multiple Mac machines beginning at $4.99.