IMHO Kentico is flexible enough to use it however you feel. The concerning part of your comment is that the clients get confused as to where the content should be edited.

If that is the case then take a little different approach to your layout and you will still be able to have your central location for doc types but they will be more descriptive. I suggest putting the content under the document it will primarily reside. For instance if you have a Home page with sliders, create a sliders folder under the Home page and put your sliders in that folder. Same would be true for your testimonials. If you have a page they are all displayed on then place a folder under the page and put all the testimonials in there. You can use testimonials or sliders or any other doc type on any other page you want, just set the source location to be in that folder under the parent.

The folder is optional, you don't need to do that, you could easily place the doc type directly beneith the parent document. One other item you can do is set the parent of your custom doc types to Folder. This way they will only be visible when adding a new under a folder doc type and not any other doc type.

Good luck