Spotlight in iOS 9 can show you search results from inside your apps. For example, you can search for titles and text of notes in Evernote, or movies in IMDB. When you tap one of these results, you go straight to it inside the app, not a tab for a webpage in Safari. This saves lots of time in terms of switching apps and getting straight to the document or information you need.
However, by default, all apps are enabled in Spotlight search, and if developers update their apps to include data in search results, their data is now there by default too. The punchline: your Spotlight search results can get cluttered fast, possibly too cluttered to be useful.
A good way to focus Spotlight for your wants and workflow needs is to visit Settings > General > Spotlight Search. There you can disable apps and their data from appearing in Spotlight. I spent a little time there, and now I find myself using Spotlight much more often to find everything from emails, to movies in IMDB, to ideas that I captured in Drafts for articles like this.
The one drawback I see so far is that if you want to hide an app’s data from Spotlight, but not the app itself, you’re out of luck. For example, if you don’t want to see email messages, but still want to user Spotlight as a quick app launcher, you can’t hide your email but still keep your email app as a search option.
I’d love to see Apple add some more granular control here, perhaps similar to Notifications settings, where you can shut off, say, sound or icon badges, but still keep banner alerts and Notification Center.