As someone who participated in "partially-structured" spring recruitment, I can say that it does help the PNAMs a great deal. All seven of the sororities on my campus participated in the big open house event which was held in one central location.
This gave me the opportunity to see ALL of the chapters in one setting. I wasn't forced to pick and choose which parties to attend. I didn't have strong preconceived notions about the chapters, but I did have some prior opinions. Other chapters I knew nothing about. Having the chance to go to an open house allowed me to meet chapters I might not have visited had I been forced to blindly pick where to attend.
.....Kelly