Personally I only own some altcoins and some BTC, its not even $300 dollars in totals so im not worried about the IRS or anything, but you never know when BTC or an alt you are holding goes to the moon, then they may be interested to know, and im worried about them asking and then seeing you used a fake name, so im using my real one. Im also worried about somewhere in the future they asking where X money came from, then I would say I had a Poloniex account, but if you use a fake name, they may ask why the name doesn't match your real name.
At the same time I also like to have privacy so using my name on this sort of crypto exchange is not something I like so I would like for alternative that don't force you to disclose name and location even if you only do small crypto currency-only transactions. I have been looking for other exchanges but their volume sucks compared to Poloniex so I have been using Poloniex only since then.