Why bother?
Because I stay focused on my client problem
As developers we like to feel smart and we like to care about our software design. The problem is that sometimes we focus too much about the software design and not that much about the problem our client or our boss is paying us to solve. UD helps me to focus.
I was working on an application I was struggling with not because it was difficult to develop but because I was currently reading a good book on software architecture and I was tempted to think about that and not about my client needs. As professional I knew that I was not acting well but the playful child inside my brain could not stop thinking about the brand new stuff. I was running out of time and I was not able to take control of my thinking.
I know you have been there.
Now that I have this templating system is much easier for me to be productive. I am not distracted because all the code that composes a page is contained in just one file. I do not need to open the usual three files (MVC) only to make a form. My brain is not distracted by computer language minutia. The look of the application is consistent and the most of the errors as human I make when I am typing code are automatically checked.
Because I keep my application tested whitout writing things twice
As developer we work for long houres. When we are tired we tend to make small mistakes, like typos, we are quickly able to solve but that lower our productivity. Sometimes those mistakes are more insidious. If we miss-type a parameter name in a link, and we do not check that link, an annoing error can be shipped to the quality control or worse to the client. It is nothing particurally hard to fix but It can really make us look bad as professional. UD had an internal system that checks this annoying things and it does not require for you to write things twice. Writing the code you automatically are provinding what UD needs in order to double check problems like that.