Why result types and display templates for word, PDF, power point and more files are different? What will be the problem if I set search results of word, PDF, power point files to the same display templates?
Different file types have different display templates because they are rendered differently in search results. For e.g. for PPT files, you get to see preview image of the pptx document. Upon hover you can also see the interactive slideshow view in the preview thumbnail in hover panel. For word document you are able to see docx preview in the hover panel. For people search, you get to see the profile image and profile properties for each search result.
If you want to use same display template regardless of the result type, you can modify the search results web part and under web part tool pane, expand Display Templates and select option "Use a single template to display items" and select the display template from the drop down menu that you want to associate for all result types.
See this link to know more on display templates and result types
- Customization of search results display can be done in single template
- Addition of new ManagedPropertyMapping can be done in single template in case your search results need to display additional properties associated with the item.
- Preview of the office documents on hovering the search results will not load in case you use same template for all the result types.