Like @byn I don't think it's going to make or break your application, but emailing POIs prior to applying can be helpful. First, you can make sure they are even taking students. If they aren't, then there's no need to waste time and money in applying to that program. Some schools post this info on their websites, but a lot don't, and it's good to check with the the POI because they may be waiting on grant funding, etc. Second, if you've contacted the POI and had a positive interaction or they were impressed by your CV, they may keep an eye out for your application.
I contacted all the POIs I was applying to work with. All eventually got back to me. Some sent a form email, but some were more personal and started a dialog with them,which I'm hoping will help.