Furthermore, LATEX warns of cross-reference labels that have not been defined. This is useful to help avoid having hyperlinks which point to nowhere.
The case of missing braces, or an unmatched opening brace, is an error that LATEX2HTML actually handles better than LATEX (or rather, the underlying TEX processor). Whereas TEX only detects an error when something else goes wrong later in the processing, LATEX2HTML shows where the unmatched brace itself occurs.
Of course if no information in the .aux file is actually used, then this LATEX run can be neglected. Also, if the .aux file has already been created, and edits are made on the source which do not alter the information stored within the .aux file, then there is no need for a fresh LATEX run (except for the purposes of error-checking).