Some function in Excel is available only when the add-in is installed. For example, Solver or the Analysis group is not avalible in standard ribbons, you need to install the add-in before you can use it. See also Using Solver.
Using the Hide command you can hide the data and formulas from "inquisitive minds". But some of them still can use Unhide command. Nevertheless you can completely hide Excel spreadsheet so that it will be needed some VBA programming to unhide it.
You can make a worksheet more visually appealing and easier to read by centering text across multiple columns. Often you do this by merging and centering the merged cells, but it is not the only option.