SpeedThe next most important search feature has got to be SPEED 🚅. Slow results are nearly fatal in any search application. Irrelevant and slow results will have your users heading for the exits.
Check out Google. They do everything they can to show results in less than one second. Studies from several SEO firms suggest that 3 seconds is an upper limit. Google likes results in under two seconds. My experience from A/B tests says users start getting agitated at around one second (the heal of the hockey stick above). You have until about 2.5 seconds to turn off the hour glass and show some results. If not, your user is inclined to look somewhere else. You don't need complete results. Offering some type of meaningful response is a critical action.
ValueIf you think of value as a metric that integrates time and relevance, you have an even bigger concern.
You have more time - but still limited time - to start offering value. Remember: Your users don't really want to use search. They want to have used it. Get them their answer and get moving. Past experience suggests that application type matters: users of complex applications are more lenient. Just watch out for simple searches on the desktop. You need to get to a good answer in 10 seconds or less. If you fail big - or fail too often - your user is not just inclined to leave. There's a good chance they will exit and never come back.
To add some urgency to the mix: Mobile users have less patience. They can leave - never to return - in as little as 5 seconds.
So don't forget to focus on search result relevance. Just make it fast.