Setting a default app for a specific file type (like JPG or PDF) ensures that when you double-click on a file, you can open it in your preferred application. Windows 10 is tweaking the way that Windows handles this process — and it sounds like an improvement.
The new behaviour is being introduced in the just-released latest preview build for Windows 10. The big change is that apps are no longer allowed to automatically change your defaults — only Windows can do that.
Here's how the new process will work. Let's say you install a new image editor. The first time you double-click on an image file after that software has been installed, you'll see a prompt asking you if you want to change your default app to something else. Newly-installed apps will be identified as such on this list. Only Windows can invoke this prompt — it can't be called up by the installation process for an individual app.
This behaviour already exists for 'modern' Windows 8.1 apps, but there were inconsistencies in how it was launched by older apps. As the Blogging Windows post announcing the change explains:
In Windows 8.1, Classic Windows applications (Win32) could invoke the prompt asking you to change your defaults, so you may have seen multiple prompts during install and after they launched. However, Windows Store apps could not invoke this prompt. Instead, a notification banner will appear after your apps are installed telling you that new apps are available and you would click on this banner to change your defaults.
Overall, this feels like a better approach to us. What do you think?
Announcing Windows 10 Insider Preview Build 10122 for PCs [Blogging Windows]