Are Tides Useful?

Yes, tides are very useful.  Though the natural occurance of tides is something that cannot be stopped, decreased or increased, people have made use of the phenomenon of tides for many advantages.

As long as people have been sailing in ships, they have noticed that vessels in the ocean have organic matter growing on the hull below the water line.  (This can include barnacles, algea, and even mussels.)  In the days of large wooden sailing vessels, sailors would  navigate their ships to a sandy beach at high tide and tie it off securely.  As the tide would recede, the ship would be effectively beached.  Then, the sailors could careen the vessel.  That is, they would actually set fire to the growth on the hull.  This would not damage the ship, as this was a controlled burn.  At high tide, the ship was untied and floated free.  The resistance to speed created by the organisms was now removed.

Similarly today, the use of tides allows vessels to be beached so that the underside, including the rudders or propellers can be maintained and/or fixed.

Of course, for large vessels engineers have since invented drydocks, allowing a hull to be exposed and dry for any length of time rather than only for a few hours a day.

For the most part, the tides exist and we have to deal with it.  In some places tides are extreme (the Bay of Fundy), in others, they barely change (the Mediterranean Sea).  For those who live/work/build near the shore, it is not a question of whether or not the tides iare useful--because, face it, we can't suddenly outlaw tides and make them go away--but how do we best take the tides into account when undertaking a building project, calculating flood zones, measuring tidal erosion, or determining a rate for flood insurance.

Even if we determined that tides are not useful, there is nothing we can do about them.  They are here to stay and we can either "make the most of it" or we can simply avoid the shore altogether.