When the boost support was added the intention was to support a usecase like
For the fulltext search on a node where the fulltext content is derived from multiple field it should be possible to boost specific text contributed by individual field. Meaning that if a title field is boosted more than description, the title (part) in the fulltext field will mean more than the description (part) in the fulltext field.
This would enable a user to perform a search like /jcr:root/content/geometrixx-outdoors/en//element(*, cq:Page)[jcr:contains(., 'Keyword')] and get a result where pages having 'Keyword' in title come above in search result compared to those where Keyword is found in description.
Current implementation just sets the boost while add the field value to fulltext field with the intention that Lucene would use the boost as explained above. However it does not work like that and boost value gets multiplies with other field and hence boosting does not work as expected