I've seen some similar discussion threads here and there on gradcafe and though I think it's better to not send them an email if all you have to say is, in a nutshell, FYI, I applied, I've seen some people find excuses to email - Questions about admissions timelines/ procedures (if your POI was answering these before). I'm really tempted to email some POIs I had positive contact with just for the sake of doing something... But I don't want too sound like I'm sucking up to them blatantly and any questions I have are more for administrative staff so I don't want to bother people who are busy reading applications... Just my thoughts...