You can start individual apps, of course. However, it’ll also help you launch pinned, recent and shared documents. There’s also a prominent search tool that can find apps, files, people and sites. You could start the day by tracking down a must-reach contact or the latest revision to a PowerPoint deck, in other words.
The Office app is free (not including the productivity software itself) and will replace My Office if you’re an Office 365 user. It’s initially reaching Windows Insider members on the Fast ring, but it should reach all Windows 10 users “soon.” The software is strictly optional, but it’ll come pre-installed on new PCs beginning in the summer — Microsoft is no doubt hoping to reel in people who might otherwise make a beeline for Google’s services.