IMO, it depends mostly on your embassy. I would send in chats, photos, passport stamps, etc. If you don't want to create 'clutter' add at least 10 pages of some evidence of communication, visits, etc.
I don't believe it slows down the process to send in more than you think. USCIS isn't actually reading the info, as far as I know, they are looking for the basics.
The reason people add more than others is because some embassies are tougher than others. Some COs do NOT care to look at any evidence the interviewee has with them during interview so the petitioner decides to add a lot from the beginning to increase the chances of the CO seeing the documents, photos, chats, etc.