To find out whether some file needs to be marked as the sparse file execute the "SparseChecker" GUI and select the file in the edit box at the top. When the file is open and the basic statistics has been displayed in the log console window press the "Analyze File" button. The analysis starts and the results are being displayed during this process in the log console. Depending on the file size and file contents the analysis may take some significant time. Check the progress bar under the selected file edit box to estimate the analysis progress. Here is the screen shot demonstration the analysis of some large file:

On the screen shot we see that the some file has been selected for analysis. The messages in the log console show the process of analysis as well as the resulting summary information. In this particular case we see that the estimated profit is about 2GB of the disk space which is currently occupied by our file. Each line on the log console informs the user about the detected zero range. It reports the offset of the range from the beginning of the file as well as the size of the range. Although this information is not practically very useful to the casual user it may be interesting for enthusiasts and researchers providing the layout of the file by means of zero ranges located in it.

In order to free these mentioned 2GB of the disk space press the "Mark Sparse Regions" button. Note that you can't do this without performing the analysis first. Marking the sparse regions causes the disk space occupied by zeros to be released.