While crossing the enemy's T is a desired goal of a lot of (gunnery-based) naval maneuvers, it's only rarely been accomplished in battle; and in perhaps the famous of all naval battles, Trafalgar, Nelson led his fleet into action while getting his own T crossed, twice.

In terms of the value of the tactic, of course, it allows one's fleet to concentrate fire on the front of the enemy line, while allowing the enemy to respond by use of their forward guns, which could be screened out of action by friendly ships ahead of them. It can be used by a smaller or weaker fleet to whittle down its adversary, which is one of the reasons the Japanese navy was obsessed with the tactic in the late 1800s through the run-up to World War II, structuring its desired battle fleet around fast ships with big guns that could dictate action and be qualitatively superior to the American quantitative advantage.

In fact, the Japanese navy was one of the first to successfully use the tactic in modern naval warfare, when Togo twice crossed the Russian T at Tsushima. Although the angles were oblique, he crossed southwesterly in front of the Russian fleet steaming in columns northeast, then doubled back to the northeast and crossed in front of the Russian fleet again, "heading" it and forcing the Russians to fall off easterly. Togo was out of range the first crossing, but was able to start hitting the Russian ships and deranging their formation when he crossed the second time, eventually trapping the disorganized Russian fleet between two battle squadrons and forcing its surrender.

In the battle of Jutland, the British Grand Fleet was able to cross the High Seas fleet's T twice (despite Beatty's utter failure to signal the German fleet's intention up to Jellicoe), but both times the German admiral was able to execute a crash turn to the south and get out of range.

At the Battle of Cape Esperance, the American fleet crossed the T of a Japanese cruiser-destroyer force, and a short, rather confused battle ensued in which the Japanese force was damaged and the American forces fired upon each other.

At the Battle of Surigao Strait, the last battleship-vs-battleship engagement in history, the American forces also crossed the Japanese T, at night, aided by radar. Radar fire control allowed the American battleships to severely damage the Japanese fleet (which, to be fair to the Japanese, had broken out of its formation such that it wasn't a true "crossing of the T" as much as "passing in front of a gaggle of ships).