It is especially important to monitor tides for people who rely on the sea for living - fishermen have to know the kinds of tides they are going to experience so as to decide whether to set off in search of fish or not. It is also quite important to monitor tides if there is some construction going on near the shore - for example, building bridges or docks, as when the tide comes, it may flood the whole thing. Scientists also study the tidal movements so as to better understand the circulation of the oceans.
Hope this helps! :)