Use a stand mixer whenever you'd like a helper to do mixing while you're occupied with another recipe task. You will save time and money by using it. It is faster and better at evenly combining ingredients than any human could ever be.
Look for a larger bowl (some stand mixers are quite small. I prefer at least a 4.5 bowl) that can go in the dishwasher, has multiple attachment options, is durable, has a tilt-head to make it easier to add ingredients, and has a good number of speed options.