It's been a busy year for Apple (AAPL 0.86%). In March, the company announced its budget-friendly iPhone SE and Mac Studio. The company then unveiled a new round of software updates across its devices in June. The latest rumors suggest Apple could announce a cheaper version of the iPad this fall, along with a 27-inch iMac Pro, with Apple's long awaited virtual reality (VR) headset possibly coming next year. 

The recent stock market rally has sent Apple stock surging, but it's still down 6% year-to-date. Even at a forward price-to-earnings ratio of 27, which is a premium to the average stock's multiple of 21, Apple is still a top stock to consider for three important reasons.

Its gigantic installed base keeps growing

Apple's most recent investor update shows that its devices continue to win over new customers. Through the fiscal third quarter ended June 25, Mac sales were down 10% year-over-year -- but more importantly, Apple reported that nearly half of the people that bought a new Mac were new to the product. 

The same trend is happening with the iPad and Apple Watch. The iPad installed base reached a new all-time high, with over half of those purchasing an iPad last quarter being new to the product, while over two-thirds of those purchasing an Apple Watch were new customers. 

Perhaps the most telling sign of Apple's brand strength is its growing adoption in the enterprise space, where companies are increasingly using Apple products as a strategy to win new talent. 

Apple has a full slate of new products and software updates on tap for the next year to keep its installed base growing. But at some point, investors should expect Apple to finally reveal what it's been working on in the transportation space in recent years. An Apple Car has long been rumored to be in development, but according to analyst Ming-Chi Kuo, Apple's car project is not just software, but also includes plans to launch a fully functioning autonomous vehicle. In March, Kuo expected Apple's vehicle to go into production as early as 2025.

That said, there are plenty of new categories of products that Apple hasn't penetrated yet that could lead to big returns for investors.

New services

With Apple generating over $100 billion in free cash flow on a trailing 12-month basis and spending $25 billion on research and development, there are obviously plenty of projects that are kept top secret at Apple headquarters. One opportunity for Apple's growing services business, which reported growth of 12% in the last quarter, is advertising.

Apple has numerous listings open for advertising positions, which means the company's next leg of growth in the services business may not be on the consumer side but within the enterprise market. The global advertising market is estimated to be approximately $750 billion, so this is another opportunity, along with transportation, that could take the lid off of Apple's growth potential. 

Evercore ISI analyst Amit Daryanani has estimated Apple will generate $4 billion in revenue this year from advertising, which is included in services revenue. Looking out to 2025, advertising revenue could grow another fivefold to $20 billion. Apple's services business generated nearly $60 billion in revenue through the first three quarters of fiscal 2022, which is primarily from the App Store and paid subscriptions.

Apple's main advantage is that it has an installed base of over 1.8 billion active devices. That's millions of customers using Apple's apps every day, where it has full control of advertising over its operating system. 

Sticky customer experience

Growth in the installed base of active devices and new products and services are two key drivers of Apple's expansion. An important third driver is increasing customer engagement with those services. On the last earnings call, Apple reported that paid subscriptions are now over 860 million, up from 480 million across the services platform over two years ago. 

The company's brand and strong stance on user privacy help explain why customers are increasingly investing in the Apple ecosystem. But at a basic level, Apple simply has the resources to keep pouring billions of dollars into new features and services to keep customers loyal to the brand.

It's difficult to imagine how an iconic brand with $100 billion in annual free cash flow can be stopped. Apple likely has several new tricks up its sleeve. The optionality for new growth avenues over time is one of the best reasons to hold the stock, and if you don't already own it, it's not too late to buy Apple.