Should we always remove the .aux file before running latex? Or remove it only if the document language has changed? The first solution may be a bit expensive in terms of runtime...
I have just checked the difference in compiling time for a large manuscript (>250 pages in print) with extensive bibtex bibliography, lots of graphics and other floats, and cross-references. I ran pdflatex first. Running it again (keeping all the files in the temp directory unaltered) needed 8.77 sec, deleting the .aux file and running pdflatex again needed 9.55 seconds.
The first solution is better, theoretically speaking, but I am not expert enough to judge. The question is what other problems can be avoided by deleting the aux file. I remember having obtained "missing \begin{document}" which has not disappeared by recompiling again but vanished after closing and reloading (viz., deleting the .aux file among others). If I come across these things again, I shall check them more closely. Perhaps some others have made similar observations...
Ekkehart
