No office worker can say they use the computer and claim they've never heard of Microsoft's Office suite, or at least one of their components (Word, Excel etc). The problem with this extensive and extremely useful suite of programs that it has a lot of components, from text editors to spreadsheet creators, that it becomes hard to manage them all, especially when your desktop is probably full of files created through them. That is where a program such as Office, also developed by Microsoft, can come in handy.
As mentioned above, it is easy to get lost in all the programs and files created using the Microsoft Office, so what Office does is pretty simple: it acts as a centralized menu for all of your official Microsoft Office programs. You use it as a quick way of installing, updating and accessing all of your Office components, as well as other administrative things, such as buying new components, renewing your already existent subscriptions, etc. Of course, you don't have access just to the programs themselves, but also to the files created through them, so you no longer have to tediously arrange them for easier finding, since they will all be available from within the same window.
You can't do anything with Office unless you connect to your Microsoft account, even if the computer itself has the entire Office suite installed since it will only open the apps based on your credentials. Thus you cannot cheat by using Office to access the Microsoft Office programs you haven't bought on a computer that has them. Aside from the features mentioned above, Office does not change in any way the functionality of your Microsoft Office components.
Given that Office allows you to increase your productivity by bringing together all Microsoft Office apps and their respective files, as well as its ability to work with all but the oldest versions of Microsoft Office, make it a must-have app for any user.