What does mapping a field to the title or text index in AI Search actually do?

[Max Nowak]

Hi,

I'd like to better understand the impact of mapping, for example, the "Description" field to the text index, and the "Short description" field to the title index. I've read the Field settings docs, which touch on this subject, but it's still kind of a mystery to me. I understand what field mapping does, and that there are text and title indexes, but I don't understand the consequences for the search results.

Assuming I add a table that inherits the task table, would adding field settings (Description -> text, Short description -> title) be beneficial, or harmful because the title and text index that are generated by default are, somehow, better?

Thanks for your help,

Max

[Shamus Mulhall]

It is recommended to include a text and title mapping for every indexed source. It helps with two things: 
1) Dynamic hit-highlighting and teaser text for display purposes 

2) Better relevancy behavior. The OOB relevancy model heavily weights title + text fields.