I do the whole stack of Web app development except graphical design. That means that I do everything from collecting requirements to writing code to setting up infrastructure to deploying to production and then maintaining all that.
The code I write is of high quality and maintainable. I'm good with OOP and my code follows the SOLID principles. This is important when a system is not write-once-then-deploy-and-forget but instead starts small and keeps evolving for years, adapting to changes of business needs.
To sustain agility and adaptability to changes of business needs, I employ TDD and Specification by Example. Using both these approaches makes it much more likely that I write the right code (satisfying business needs) and the code is right (correct technically).
I have experience with high load systems and know how to set up and maintain them. Many Web applications need to support millions of interactions a month, and sometimes even a week. Without explicitly preparing a system for this kind of load, it will basically grind to a halt when all those users/customers come.
I also have experience with setting up high availability clusters to keep an application up and running in the event of hardware failure. Without high availability, when a server or just a component of a server dies — and that pretty much happens every day on this planet — users/customers will experience downtime until a human migrates a service to functioning hardware. Highly available systems recover without downtime or with just a few minutes of downtime without human intervention.