Daily Class Achievement and Practice Mode
I understand what you mean but the additional benefits of playing unranked/ranked is that you will get much more experience playing your class. It helps build on the pvp skills that are required to play unranked/ranked unlike hotjoin which can be taken non seriously since players come and go. Unfortunately you can not get this from hot join.
Also you get points towards you achievement this way as well. I however do hot join for my dailies its much faster.