A lot of (digital) ink tends to get spilled about how much businesses grow their revenues each quarter. But sometimes, like with InMode's (INMD 0.70%) second-quarter earnings, the most exciting figure isn't the top-line sales. 

Instead, there's a certain component of the company's revenue mix that has far bigger and even more positive implications for its future performance. So let's learn which metric I'm talking about and why it's important for anyone considering an investment.

More demand for beauty treatments means more sales of devices and their parts too

InMode makes workstations that plastic surgeons and other clinical practitioners of medical aesthetics use to reshape figures, tone muscles, eliminate fat deposits, and remove unsightly hairs, among many other applications. Customers first buy a workstation for their clinic, then they also buy accessories and consumable products that are necessary to provide treatments to people. Many of the consumables are items like cannulas and treatment applicators intended for one-time use.

The more customers use InMode's devices, the more consumables they need -- and the more they'll need to buy in the future to keep offering those same services to their patients, too. Therefore, growth in sales of consumables is a great proxy for how much demand customers experience. It's also an indicator of whether they'll be interested in buying additional accessories and workstations down the line.

So that's why it was great news when InMode reported that in Q2 it earned more than $21 million in revenue from services and consumables, marking a 44% jump compared to a year prior. That percentage-point growth is the one big reason to buy this stock because it shows that customers are using their workstations more and more over time. For a company with a razor-and-blade business model like InMode, seeing big growth in recurring revenue segments is a big plus. And the company hasn't even fully penetrated the global market yet. 

There are a few other figures to keep an eye on

So InMode's engine of recurring revenue is revving up. But it's also having no trouble chasing top-line growth and maintaining its profitability at the same time. Its quarterly gross margin actually edged up by 1% in Q2 compared to a year prior, leaving it at an admirable 84%. That bodes well for its bottom line expanding significantly as it spreads out its sales operations around the globe. 

In total, it pulled in just over $136 million for the second quarter, meaning that consumables and services account for around 15% of its revenue. And management anticipates that as more of its devices are installed worldwide, its proportion of recurring revenue will rise. Given that it's still shipping plenty of its workstations to new and existing customers, and that it's developing even more consumables and workstations to sell, the company's long-term earnings flywheel is now in full motion.

To sweeten the pot even more, InMode also has zero debt, and it's hard to imagine why it would need to take on any new loans anytime soon. In other words, there's nothing in the way of the company committing all of its resources toward growing even more, all while profitable. And that's another reason the stock is worth buying. 

Of course, this isn't a risk-free investment. There is always the chance that another medical device maker will be able to funnel sufficient resources to its research and development (R&D) operations to create superior products that ultimately steal InMode's market share. But as of right now, that hasn't happened yet, and even if it did, it would likely take a few years for the competitor to catch up.

So I'll be buying more shares of this company in the near future, just like I've been doing over the past few years, and you might want to as well.