As a front end developer, I sometimes need to make the call of how a certain page/application state will look like.
One of the best ways to design a ui is to create a wirerfame first.
Some of the benefits of using a wireframe:
It organizes the workflow
Saves some times on decision making
Might help other team members
When developing code - it may help in the developing process in the oop concept.
When using the right tools - it's flexible to change or create different concepts, i.e. - for the same page you're dealing with.
Whether you design a website, a web application or any idea you have in mind - wireframe is one of the best starting points.
Here is a link to a quite thorough article/guide on wireframing tools - both free an commercial.