A family of Microsoft spreadsheet software with tools for analyzing, charting, and communicating data.
Generally, if you have set a row height manually, or if you have merged cells in your row, AutoFit will not adjust row height. This is by design.
In practice, depending on what "never seems to work" or "work properly" means for you, the displayed or printed results of AutoFit also can get poor results depending on your zoom settings, or font settings (especially if XL has to do a font substitution), or your print quality settings (set in the Page Setup dialog).
Results are generally better if you (a) stick to a font provided by MS, keep both display and print zoom at 100%, keep your print driver updated (it affects screen display as well, since XL uses the print metrics for screen layout), and adjust the print quality to be optimum with your particular printer.