There are several. One is the Sewer Solution which is water powered. A lot of people have good luck with this, but mine jammed on me the first time I tried and I've never dared try it again. There are a couple of temporary 12v motor ones; I have one of these and it works great. There is also at least one built in system, but I don't have any experiance with it
The advantages are 1) no 3" 'slinky' hose, it uses a 1" or 3/4" 'garden' style hose. 2) it can pump the sewage a long distance or even uphill. The disadvantages are that it requires either water or power, and tends to be slower than a standard dump. So no, it is not necessary, but sure comes in handy sometimes.