Are puddle flanges(for GRP pipe installation) used to prevent wall cracking? Or just to restrict the flow to other (external) side of the wall?

Puddle flanges are there to stop any flow of liquid from one side to the other of a wall of some kind and to act as an anchor on any material. 

Puddle flanges (GRP pipe installation) are used to secure the concrete structures from sudden impact of a vibration (seismic) Yes, wall cracking is one.