There are certain important reasons why using a web framework during development is important. However, using a framework cannot be said to be absolutely necessary, but it can really help you as a developer to build your applications fast. If you care about saving time building web applications, then using a framework becomes a no brainer.
Faster Web Development
Rapid web development using a framework is achieved by the use of ready-made libraries within a framework or even by pulling in and re-using generic modules. The idea of a framework is to prevent reinventing the wheel. A framework like PHP Laravel comes along with a prebuilt authentication system which saves a lot of time enabling you as the developer to focus on other aspects of the application you are building.
Better Application Development
Using a web framework in your development makes your code better. Better because the framework guides you toward complying with the business rules. Your code will be structured in a particular standard say in an MVC (Model View Controller) format. This will result in your code being of high quality, easy to maintain, and easy to upgrade. Software that has been developed using a framework is well-thought-out and can easily work with other softwares within the market as they tend to comply with market standards.
Longevity of Web Applications
If a developer builds software without using a framework, especially one known in the market, then it can lead to a situation where only that specific developer is able to maintain, upgrade or even add features to that software. This can be bad for business especially if for one reason or another the said developer becomes unable to work on the software. Such a situation can harm business operations. That can be avoided by the use of a framework so that an application can be taken over by another developer with relative ease.
The use of a web framework guarantees the longevity of web applications due to the application upgradability, maintenance, and relative ease of availability of web developers to handle web applications built using a framework.