I like that it's easy to use with many built in functions as well as addons available both free & paid versions which makes this an ideal program if you're looking at multiple options of calculators or just want something really simple but effective! It also has some great tutorials included so there isn't any learning involved once setup (which takes about 5 min).
There are other programs out there better suited towards specific needs however when searching around they don’t always have all features needed - especially not those offered by MCalC such as AUC/ROC curves calculation capabilities. This tool can be used across our department without issue since everyone knows how to operate Excel / Word and most people own computers anyway.