(a) Tidal pools have formed a habitat for specially-adapted organisms such as starfish, sea anemones, mussels, and clams. Thus the tide contributes to biodiversity.
(b) The ocean plays a big part in moving heat absorbed near the equator to the subpolar latitudes.
Since ice ages are believed to be triggered when it's "too" cold at 65 N, the transport of heat plays a part in stabilizing climate. MIT oceanographer Carl Wunsch argues that the tides provide much of the mixing that facilitates the ocean's transport of heat.
(c) In some topographies, the tide can provide a power source. This idea has been put into practice successfully in the Bay of Fundy in Canada.
(a) Like any movement of water, the tide facilitates erosion and changing coastlines. This may actually be healthy for the earth, but it's not so good for human communities that have made economic investment in structures near the shore, or who want to preserve particular estuarine environments (because the humans have ruined so many other estuarine environments).
(b) The tide can amplify the effect of an extreme weather event such as a hurricane.