Monolithic anchors - using a boulder (best practices)

I’m trying to get more comfortable with improvising anchors in the alpine and am wondering how everyone approaches belaying or rappelling off of natural anchors - in particular how you rig a boulder or tree anchor and, if necessary, equalize them. I understand that, for bomber trees or boulders, you can get away with wrapping a sling or a cordelette around the feature and call it good. But I’ve also seen examples of people adding redundancy to the system. I’ve attached a photo I found of someone’s rappel set up that I can’t make heads or tails of… how did they rig this? Why? What does everyone feel is best for situations like this? 

This isn't meant in a negative way, but if you can't figure out what is going on in that picture, you really need to buy a book that covers the basics of building anchors, or better yet ask someone to show you a few things in person.

How could someone answer what is best? From just that picture you can't even make a judgement on the security of the block at left so anything else is just speculation.

You can see both ends of the single cord they creatively tied so as to provide redundancy against cutting of a single strand. Maybe that should be your takeaway. A common trick is to tie an overhand at either end of a long sling, this creating two independent strands. That is basically what you see here.