For DrK, yeah. For hero and paladin, not really needed but usefull. Less chance of dying as you can tank more hits. Also less pot burn. DrK needs it because they need to be below 30% of their max hp to activate berserk, which gives them more dmg.
If you dont feel like washing at all, you dont have to. Having 15k+ is quite usefull to tank several zakum body hits and 2 BF hits.