Screen Sieve allows users to locate occurrences of characters or words in the current window. When a search is performed, the utility fades the entire screen and for each letter you type, it highlights results in real time. The application is designed to speed up your productivity; in order to achieve this, Screen Sieve's search function is triggered by a custom hotkey.
With this tool, you should be able to find data easier on your disk; but that's mostly in theory. When compared to Finder's search function, Screen Sieve has its advantages as well as disadvantages. Screen Sieve works with multiple types of applications (Mail, Safari, iTunes and many other apps written in Cocoa). In spite of this, Finder will look up data from all over the disk (not only the frontmost window) even though it is restricted to its own window. Moreover, whenever you perform a search with Screen Sieve, a full-screen fade will cover all your screen making it impossible to perform any other action.
Considering that most programs come with a search function of their own (which is usually triggered by a similar keyboard shortcut), Screen Sieve's functionality is generally unneeded. If however, you enjoy full-screen fade effects, you may want to give it a chance.