1script - 5:38 pm on Sep 2, 2010 (gmt 0)
And helps Google to ease the CPU load by letting them cache results of much fewer queries. Additionally, having fewer word in the query in the first place makes building the SERPs a less intensive CPU task - also a welcomed characteristics for an overloaded Web property.
Suggest can paradoxically lead to more searches for the general phrase... not the disambiguated phrase that might have been searched without it. This can also drain off a lot of traffic.
I plan on experimenting with search suggestions on my own sites for exactly the CPU load, not necessarily user experience reasons. Site searches are very burdensome and I've seen many sites resort to putting captchas and other means of slowing down search requests. I would much prefer to gently nudge my visitors to search for terms that have already been cached instead.