It's useful to see how your order volume changes over-time. It'll give you a different perspective than total sales. Combine the two you can learn a lot about your overall business health.
If your order volume has increased and your total sales have increased, you're growing.
If your order volume has increased and your total sales have decreased, you're picking up more, smaller-amount orders. That might be a good or bad thing, depending on your overall strategy.
If your order volume has decreased and your total sales have increased, you're pickup up larger orders but less orders overall. Again, that could be good or bad depending on what you're trying to do.
If your order volume has decreased and your total sales have decreased, you're seeing business contraction which could be a sign of a problem.
Order volume alone can be very cyclical though. I found averaging it across months to work better, especially with 3 or more months at a time. You'll want to take a wide enough view so that your spikes don't sway the number too much. Ideally a full year.
Each account in Repeat Customer Insights comes with order volume tracking and does all of the averaging math for you. It's in the Store Analysis in the Average Orders per Month metric.
See how the month a customer orders will change their behavior
Repeat Customer Insights will automatically group your customers into cohorts based on when they first purchased. This will let you see how the date customers bought would impact their behavior.