Symfony framework comes with built-in security and scalability. Advantages of using frameworks are huge eg: Tasks like filtering and validating user input are built-in. Regarding scalability, Symfony is designed to grow, which provides a stable structure that you can rely on, no matter what the size of your application or the traffic is. This makes Symfony the ideal solution for very complex and large scale enterprise project. 

The common code structure in Symfony enables collaboration. If someone else knows the framework that the application was built in, they can use their understanding of the structure to quickly adapt and contribute.

Symfony is a very flexible framework that can be used in different kinds of applications. It's also very modular, to the point that you don't have to use the entire framework if you don't want to, only bits and pieces if you're so inclined. 

Symfony also comes with an easy integration to automated testing tools like PHP Unit. It's also very well documented with a very active development and support community. Symfony is available in a number of different editions. For most applications, the standard edition is the most appropriate. Standard edition comes with a collection of the most common components, ready to go, and includes a built-in configuration system. There are also a number of Symfony distributions available, think of them like starter kits. Similar to Linux distributions, Symfony distributions are purpose-built with a particular goal in mind. 

Finally, Symfony is available as individual components, not just as a bunch. Each component is a decoupled group of standard features, meaning that a component doesn't actually have to be interacting with Symfony, they are all stand-alone. Within the various editions, Symfony also has a highly structured versioning system. 

Symfony version 4 is the current major version, with minor versions being released on a schedule of every six months. Symfony also provides long term support, or LTS versions that are released every two years. Each LTS version provides an entire three years of bug fixes and four years of security fixes. That's something that can be relied on, and definitely something to consider when choosing which version to use. 

The upgrade process between minor versions is very well documented. Symfony includes a lot of instructions, and details on what changed between each minor version, which makes it easy to upgrade, incrementally between each release. As you can imagine, there's a lot of choice when it comes to Symfony. 

These are few among many reasons to choose Symfony as the ideal framework for developing your future web applications at an affordable, scalable and in a secure way.