Server controls are meant for eliminating redundant code and boosting productivity. They make development tasks easier by hiding their internal details and providing ready to use packaged functionality. There are many controls shipped with ASP.NET that shorten development effort, but there are always opportunities for us to build our own controls to reduce even more development effort. Many times business scenarios create the need of custom controls to simplify development solutions.

If you want some reusable functionality in a single application or for few developers and it can be achieved from combining existing web controls then user controls can be a good choice. But when you want to make a piece of functionality reusable and redistributable then custom controls will be the best solution. You can extend some control or make one from scratch or combine multiple ones as per your need. This activity will let you get into the things and will add confidence for bringing novelty and uniqueness into your projects. Most importantly, you will become adept at intrinsic details of the architecture of the dozens of standard controls shipped with ASP.NET. The purpose of these controls is to achieve a different functionality (from the existing server control), a totally new functionality, or a combined functionality of several other existing or new server controls.