I, too, had a hysterectomy. I was in my early thirties. On occasion, I voluntarily discontinue HRT, but I usually end up right back on it. Without HRT, the symptoms of hot flashes, night sweats and mood swings is most prevalent.
As far as how necessary it is to take it, I think it really depends on your age, the intensity of symptoms and the reason for the hysterectomy in the first place.
If you decide to discontinue it, check with your doctor first. Most physicians do not have a problem with a patient who prefers not to take it. Immediately after a hysterectomy, however, it's generally best to have some form of HRT so the change is not so abrupt.