The main aim of the expedition is to explore new passages - to boldly explore what noone has seen before. Indeed, in many cases, what noone even suspected was there. This is the fun and excitement of expo, so why spoil it all by doing tedious activities like surveying?
Once upon a time, none of the caves were explored. Anything you found was guaranteed virgin. Now, many of the obvious caves have been looked at. Some went, some didn't. The fact that you can come to Austria and be pretty sure of finding new passage to explore is all down to the folk who came before you recording what they looked at, both the stuff that went, and the stuff that didn't. Without detailed recording and surveying of the caves, it would rapidly become more difficult to find new passage, or to be sure that round the next corner wouldn't be a load of previous explorers' footprints.
A lot of work is involved in maintaining the lists of caves that didn't go, the lists of going leads, the cave surveys, the route descriptions and other documentation. In the very earliest years, this work was not regarded as a priority and we are still living with the problems which this created. In the UK this work is done by a dedicated few souls with a long-term commitment to the Loser plateau. To make their job easier, indeed, to make their job possible, and thus to ensure that future expeditions have new passage to find, those actually exploring the caves need also to survey them and to record what they looked at in a variety of other ways.
Of course, its also rewarding to have a big survey or a cave photograph on your wall and to be able to point to it and say "I found that !" Good documentation is also essential to ensure that the club appears competant when applying for Sports Council money and the like. Indirectly, surveying makes your holiday cheaper.
Surveying ethics. Survey what you find - don't leave it for someone else. For horizontal stuff, it is usually most effective to survey into virgin passage. Don't run off finding loads of cave and then survey back - this leads to long nights and eventually to poor or incomplete surveys, and probably to missed call-outs. For vertical stuff, where rigging is time consuming and you don't find too much in one go, surveying back is probably warmer, but if you run out of time, energy, morale or lights, make sure you go back and survey before derigging or pushing more!
One great advantage of doing the surveying yourself is that a surveying party inevitably looks more closely at a passage than an exploration party. This means you are quite likely to find new going leads as a result of doing the survey. As evidence for this, at one time, the University of Leeds Speleological Association found more passage in Yorkshire each year than most other clubs put together. The reason - they had a program of systematically resurveying known caves, and invariably found previously overlooked ways on.