pretty sure google will get you the docs from IBM , but I can share some of our experience with HADR as we have had it in place in our prod env for a couple years.
I wouldnt want to support critical databases without it anymore. We have had quick recoveries from real production outages that in the past would have been very painful and lengthy, but our hadr standby was able to bail us out.
We dont see performance impacts when we are running it.
Only con in my opinion is cost of hardware to support it.