Maybe "as prepared set"
Maybe you should adress this request to the developer forum to get a betteranswer. Anyway here my two bits:
a) You are right, the file is used by Baan for sorting etc.
b) It usually gets so large, if Baan sees itself forced to basically dump the complete table to get a consistent view on the data. This does not only create a huge file, but also slows down the whole thing.
Sometimes this is even enforced by the programmer, by using the "as prepared set" in the select statement. Some time ago, Baan advised programmers to use this statement to avoid the "Snapshot too old " error in baan together with Oracle. In my opinion this was a pretty stupid advise and there are other means around it.