When it comes down to the daily, day-to-day running of your business, you rely on applications. While the hardware, the OS, the network, the internet, etc, all have their place, applications are pieces of code that directly correspond to you. They accept your requests, direct it towards the operating system, which directs it towards the hardware, and the hardware carries out the instruction.
As you can see, applications are absolutely essential. Without them, all your complex hardware, software, and network systems would be essentially useless. There are several applications you use daily for various purposes. Maintaining them becomes essential for the smooth functioning of your IT system.