We love trigger words because users love trigger words. Good trigger words improve the 'scent' of a link enormously.
It is a word or words associated with a link to make it clearer to users the type of information they can find beneath a link. Gerry McGovern calls them care words, other people call them trigger words. Go to the BBSRC site and you will see that under the link 'Our Organisation' they have the words: Structures, Policies, Institutes and Centres, Spending, Achievements, and Jobs. These are the trigger words.
Well the amount of scent that the average link, of one or two words, in the main navigation of the site can give off is limited. As work by UIE shows the best performing links contained 7-12 words - difficult to fit that many onto a tab. Therefore, by adding trigger words - based on user research identifying the words and language that are meaningful to users - you can get the link to give off a lot more scent for a wider range of goals.
For example, you will notice on the BBSRC site that the trigger words are not links, we think making them links is a bad idea. We know it may add another click to the user journey but we don't think that matters. If they are made into links users will go straight to the content page and miss the navigation page at the next level down. While this may be good for some users, for most users it is better for them to see all of the options in the navigation page because they are then more likely to get to the correct information for them.
User satisfaction is more strongly correlated with the confidence a user has they are going in the right direction than in the number of clicks it takes to achieve a goal. So as long as the link plus trigger words gives of enough scent then the extra click doesn't matter.
However, something else that came up recently in some user testing is that you should not have too many trigger words. If you do, users may think these are all the goals they can achieve under this link, rather than simply being a way to demonstrate the types of goals that can be got to via the link.
So if your information architecture isn't working get thinking about those trigger words - users love 'em!