By using references to worksheet ranges as part of the array, an array formula in a single cell can fill many cells with data. It's much easier to correct errors in that single formula than to do so in many cells, even with features like Excel's auto-copy to make the job easier.
GS-Calc is loaded with functionality, but hides the full list and all descriptions in the dialog box you can use to enter a function. The description and examples contained for each function in this dialog is thorough, but this is the kind of information that should be in the Help file. Having it in the dialog is a very helpful addition to having it in the Help, but it isn't a replacement for it.
Version 10 of GS-Calc corrects one of the flaws of Version 9: The screen redraw and interface responsiveness is much better, without the flicker effect sometimes seen before. It still retains some of the interface oddities, such as numerical overflow going to the left by default, rather than the right, or the workable, though non-standard, use of the Ctrl key to select cell addresses while entering a formula.
Other improvements to GS-Calc 10 include a compressed, proprietary save format, in addition to the ODF (Open Document) format, and the ability to add a note file to each document, which can be displayed in the bottom or left panes. The notes are linked to the entire document, not to any individual sheet or cell. Cell deletion has been made more flexible, as well. These are "quality of life" improvements, small changes that enhance the application without massively changing the user experience or basic functionality.
GS-Calc also features support for pivot tables, allowing for the easy creation of summary reports and breaking down data into various categories. Charting, both 2-D and 3-D, is also supported. While it doesn't contain any revolutionary breakthroughs, the charting function has options for user control and styling of the information presented, and the interface is generally clear despite there being many possible values to adjust.