When you add a profiling attribute to an element, consider whether the document will still be valid if the element is deselected during profiling. Even if it is valid, make sure the document will still make sense if it is profiled out.

Don't try to use multiple title elements at the same location. The DTD permits only a single title in any element. Instead, use multiple phrase elements within the single title element, and put the profiling attributes on the phrase elements.

Alternatively, you could exploit the fact that DocBook info elements such as chapterinfo permit multiple title elements. You could put multiple profiled titles inside the element's info element. In either case, make sure only one of the titles is selected during processing.

You cannot have duplicate id attributes in a document. If you need to put an id on a chapter, section, or figure for cross referencing, then you can't have multiple versions of that element with the same id. You'll have to create a single element with the id and make the content of the element conditional. It helps if only part of the content needs to be conditional.

Nesting conditional elements adds significant complexity to your document. You have to consider each combination of profiling values to see if it will be valid and make sense.