Mobile testing, desktop testing and web site testing are different types of testing activities and each type has its peculiarities.
Web applications are usually meant to work with many customers in various environments. It is very important for a web site to cope with these tasks.
That is why web site performance issues must be considered during the development and testing process.
Web sites are often created in little environments with minimum hardware. A web application may have one web server and one database server. Many companies consider such amount of hardware sufficient and economically feasible during the development life cycle and first time after release, when few customers use the site.
The number of users will grow and together with it the load on the application will increase. To cope with the load the site will need more hardware. If not, the customers will experience inconveniences, such as low speed of page loading or time-outs.
If the addition of more computers is allowed by the application structure, it will be easy to increase the application performance. Otherwise a software testing company will have to do significant modifications of the web site structure in order to increase its capacity. It is always expensive and time consuming.
To avoid such inconveniences it is necessary to plan carefully web site testing and make sure that load testing is considered in it.