Big waves are fun - for surfers. For seafarers, coastal equipment designers and inhabitants, they are potential dangers that have to be taken into consideration. Altimetry cannot give the wave heights every hour - at least not without many many more satellites, but it is a good technique for identifying trends and gives us some idea of the minimum and maximum heights.
The North Atlantic may not be the roughest part of the ocean (which is in fact the Southern Ocean), but it does have the most marked variations, and its coasts are quite populated. The British Isles, along with Brittany, bear the brunt of ocean storms so potential damage has to be assessed.