[Zope] Catalog reindexing: field by field or not?

I notice that when calling manage_reindexIndex with several indexes, it will simply call reindexIndex once for each index. The question is, is there a performace penalty for reindexing several fields separately like this, or will it always be faster to only reindex the relevant indexes? It seems to me that at some point it should be faster to just reindex the whole catalog, since that just traverses through the objects once... (This is Zope 2.6, btw, maybe it's changed in 2.7?) //Lennart