There are actually two reasons to go for a headset with active noise canceling. The possibility of hearing issues has already been mentioned, I know that many pilots have flown without ANC for years and have not had any issues but then again, some have. As you only have one set of ears, it is worth looking after them, if you ask me. The second selling point, which isn't mentioned all that often, is that it can really reduce fatigue. Listening to a constant noise means that your brain is constantly processing, which uses energy. The less noise, the less energy spent and I have found that I have stepped out of aircraft with lower fatigue levels after using an ANC headset, when compared to flights where I didn't have this luxury (usually because I forgot my spare batteries). Because of this I have also taken to using a Bose QC35 whenever I'm sat in an airliner. For flying, I use a David Clark H10-13X.