Does Maplex labeling benefit from indexing attributes?

[MarcoBoeringa]

I have been wondering if the Maplex labeling engine actually benefits from indexing. Since ArcGIS for Desktop layer files work with "label classes", that can have an associated SQL Query, I wonder if indexing the specific field(s) referenced by the SQL Query, speeds up Maplex labeling. E.g. let's say I have a SQL Query set like:

"highway IN ('motorway','trunk')"

is it worth indexing the "highway" field in this case, assuming I may have large layouts (A0), potentially containing hundreds of objects to label?

I assume the primary filtering is simply spatial, so is the hassle of indexing attributes worth the effort for Maplex?

[MarcoBoeringa]

I now actually found some hints to an answer of this question in the Help, at least related to map services:

10036: Label class value has an SQL query that references field names that are not indexed

10037: Label class value has an SQL query that is not optimizable

It does seem that the label classes SQL Query usage at least in some cases gets optimized, although in the second case, this does not so much seem related to indexes, but to the number of database queries a SQL Query causes through the drawing engine.

It does seem though, that with the default "spatial index first" setting for rendering by the drawing engine, the benefits of an additional indexed field, may be minimal, but I don't see any real reference to this in the above links.