Did you know that Alfred can remember queries you've recently typed?
Once you've enabled this feature, you'll have access to the latest 20 queries you've typed in Alfred by pressing the up arrow. You can even have the most recently typed query automatically populated when you reshow Alfred within 5 minutes.
This is particularly convenient if, for example, you're making a calculation that requires a few numbers from different sources.
Type the first few numbers, go back to your other application, then pop up Alfred again to carry on with your calculation.
You can enable this feature in Alfred's Advanced preferences:
Simple and practical! :)