benefits, depends on the fair in question and the difficulty / costs it takes you to attend so.
my personal experience of Cologne once and Essen many times:
Cologne is a very big event with all the big publishers... they have large booths with all kind of shows/presentations going on.
if you are willing to wait in line for an hour or two you get a chance to play a level / get a demonstration / or at least see an exclusive video with in-game-footage of mainstream games, RTS, FPS, MMOPRG, etc in the making that will get released in a few month or even a year or two... also if you like to test the latest Wii-controller gadget, guitar, motion-tracker, etc. for upcoming and existing
consoles, then its the place to go. There are also give-aways, lotteries to win,
...and professional booth-babes ;-) of course!
Essen, is a much different event, more like a convention for (mostly family style) board games.
But there is one hall that had a special atmosphere.
Here are all the LARP-player, Games workshop et al., Wargames outlets located.
this is a real public trade fair, you can buy stuff with large discounts, find exotic old and new boardgames/PC games.
you have a 99% chance to ge a personal demonstration of upcoming (Matrix/Slitherine) games,
chat with an alpha-tester, a developer, the decision makers ...or even The Boss of a smaller-publisher.
There are not much 'hired booth babes' but a good portion of freaks of both genders dressed in handmade costumes wander around... and the non-wargaming stalls in that hall give an interesting mix also, you can test Met, check out iron or plastic swords and armors, see/buy lots of 'medieval' day to day goods, interrupted by some small company selling miniatures to paint from 'Stone-Age' to 'Cyborgs', you get the idea...
you can also do some 'social studies' and will see the real life expression of: Sheldon, Leonard, Howard and Raj ...no Penny so ;-)
...at one booth in a neighboring hall dedicated to comics was a mediocre looking bored girl on a pod hired to get a fantasy cover-all body paining. The flog of either mostly heavy over- or under-weighted nerdy guys, aggregating around that pod, all with one hand erected to get a little shaky picture with their cellulars was 'funy, surreal and frightening' all at the same time... (and a give-away of maybe 'Axe-deodorant' wouldn't have hurt that spot too) ;-)
also funny, if you see ppl 'out of role' ...People, dont dress up like an Elb, when you have the figure of an older Hobbit ...LOL