Now you can use these operators without having to press Enter or click the search button. The main advantage is that you can adjust your query and see the results as you type. Unfortunately, the results aren't displayed instantly.

Yahoo would not let us ship LiveSearch on yahoo.com or as a part of Yahoo's search engine. Instead we were only allowed to launch it on AllTheWeb, a smaller, lower-traffic search engine that Yahoo had acquired years earlier and largely left to atrophy. (...)
You have to remember that, at the time, Yahoo's search business was doing just well enough that there was very little institutional appetite for product risk. As a result, "big" or disruptive ideas were too often left to whither on the vine. By focusing on the local maximum, Yahoo unwittingly traded innovation for incremental optimization.
LiveSearch was thus relegated to a tiny test bucket of users who didn't actually use Yahoo's search product (or any modern search engine). Usage data from this flawed test was used to internally evaluate its success in comparison to the model it was actually trying to disrupt. Lacking high-level support for its larger vision and starved for resources, LiveSearch was understandably put out to pasture.