How do memories affect the path? If one has recollection of memories that were experiences of pain be it physical, mental, emotional, how do these affect the path? 

Often memories are triggered involuntarily and more than often they surface when reflecting.
In terms of how they affect the path, obviously, these are holdbacks. The goal is to get free from them.

Here is the instruction I received from my teacher about this:

In meditation, when memory comes up, do not replay the event that caused the pain. Do not think about it, thoughts don't help. Instead, stay with the pain itself. Feel it in your body. Stay focused on it and get a full taste of the feeling, thoroughly. Then go inside the feeling. Accept it and feel its texture, thoroughly. Despite the pain, go all the way inside until you get out on the other side. Accept. Go through.