That's the only way I make up Indexes and ToCs, as they don;t create the issues that using Words automatic heading style generating ToC will when making an ePub file from the Word file. One thing that gets me occasionally is that the bookmark name must be all one word, lowercase.

Are you, by chance, "Indexer," the original poster in this thread?

You do not need to use built-in heading styles to generate an automatic ToC in Word, although it is easier. Might one inquire as to what the problem is with using the built-in heading styles?

Do you use Index fields or bookmarks? These are different creatures.

No, I'm RSutton, a newbie here at least. The only issue I've found occurs when you are exporting your Word compatible format file out to mobi or ePub production formats. The heading-derived indexing is lost. It may be because the conversion software can't easily import a regular Word file (2003, 2010, etc.,) and needs a '97 compatible format. ePubs have other format restrictions, too, but in an eBook a working Index/ToC is critical. So I do it the old-fashioned way, manually, using anchors on Chapter Headings and internal bookmarks to the chapters linked back to the ToC page. Takes a while, but it works. Of course, if you're just using your Word file to create pdfs, or sharing it in Word format, none of this matters.

1. Indexing is not based on heading levels nor on bookmarks. It is based on an Index Entry field that is not a bookmark. Again, I know of no way to create an index based on bookmarks. It seems like it would be even more tedious than simply marking Index entries. Indices - Complex Documents Perhaps marking as an index entry is what you are referring to when you say bookmark.
2. Both the Index and ToC are fields. Those fields can be unlinked before you publish so that they are text rather than fields. Of course, once unlinked, they no longer will automatically update.

I have never tried to convert to epub format.