No, it's not necessary. For buyers it is massive overkill. For vendors it may be useful, but really the chances are slim that LE is going on a fishing expedition for random Tor users, or performing a correlation attack like this: http://dkn255hz262ypmii.onion/index.php?topic=159722.msg1129048#msg1129048 Bridges may be just as effective at hiding your Tor use. You can get IPs here: https://bridges.torproject.org