2. Generating Value From Excel

Excel is ubiqitous and that provides great value. Excel is so common not simply due to Microsoft pre-installing it but because it is powerful, graphical, flexible, relatively easy to use and can be a common skill expectation on both junior and senior staff.

When to use:
Almost always. It's a fantastic software that should be you and your teams default answer to any analysis.
The internet and YouTube in particular host a treasure trove of tutorials and guides that you can assign or suggest to your team to help them solve more complex tasks within Excel. The picture below shows a dashboard (dummy data) I've created in the past that combines data from multiple sources to produce a one stop shop of financial performance of a geographic area of a business. The flexibility and ease of moving objects in Excel turned this into one afternoons work.

People make fun of Excel - Why not to look down on it:
Fair or not, a lot of people dismiss excel as out-of-date for current mobile computing trends and bemoan it's lack if interactivity. Also anyone who works with data has inherited an Excel from a previous owner which has near infinity formula's and calculations that are frankly impossible to track. The result then is scrapping the old Excel file and constructing a new one which will inevitably be scrapped by the next person who inherits it, this is a big amount of time spent re-developing something that has already been solved.
With all of that in mind, Excel can handle 90%+ of the tasks that every business needs to perform. It contains simple practical functions but can also let you use if statements and macros which can replicate some of the strengths of more complex tools like R or Matlab. Recent versions of Excel also have more interactive features like Sliders that enable dashboard building. Excel also lets you have data, calculations and output methods that are all on screen at one time unlike other tools.
In short, if someone comes to you pitching a new tool and are rubbishing Excel, keep an open mind but really ask them to prove why this is a significant improvement on Excel and challenge them because the cost to your organisation to transition even part of your processes to a new tool will be significant.

I am a fan of Microsoft's Power BI though as a step forward but only as a support for Excel, not a replacement.