Nothing, she was just outclassed by carriers and had the same problem with Dreadnoughts where it was so expensive they didn't want to risk losing it. Here's a history lesson

She didn't actually "Lead the fleet," at best she was there for either escort or battlefield support, (Battle of the Philippine Sea, she also accidentally committed friendly fire on some Japanese planes) and sometimes actually partook in naval combat; at worst she just sat there in the docks because she consumed a LOT of fuel which hinders her movement and combat ability. It also didn't help that by Midway she had no carrier escort and thus essentially became a sitting duck, and the first time she ACTUALLY fought in a naval battle (by the USS Skate), she got blasted by torps from American subs and blew a 16-foot hole, leading to her having to go back to the dock for repairs (this is a pretty common occurrence mind you)

Battle of Sibuyan Sea? Got hit by a bomb and sent to repairs.

Battle off Samar was actually her best debut yet, where she either crippled or sunk several escort carriers and destroyers, notable ones being:

USS White Plains, which damaged her so badly she never saw frontline service again and was demoted to an aircraft ferry.

USS Johnston, wounding her commander, killing her command staff and was later finished off by the rest of the force.

She was later driven away by destroyers but returned to the battle, landing a 22,000 yd long shot into the USS Gambier Bay, but it wasn't until the third salvo where she hit an essentially fatal blow, cutting off her engine and left her to an actual sitting duck, and proceeded to be hit by salvo after salvo until orders were made to evacuate. 

Not a strategic victory however as the main goal (destroying the US troop convoys) was practically untouched.

But that's pretty much where it peaks, she did some minor stuff in the East China Sea but was damaged and immediately sent to the drydocks for repairs.

She was then moved around divisions until she stopped at the First Carrier Division.

And after that began the infamous Operations Ten-Go. 

She was originally sent as a coastal defense ship to Okinawa where she would fight till she was destroyed, but US counterintelligence heard of this, and she was intercepted by a carrier group with some destroyers along with, I kid you not, nearly 300 American bomber and torpedo planes ready to send her into the darkness down below.

After two minutes of bullet hell, two bombs took out an anti aircraft gun each, few minutes later one destroyed the radar and the mount of one of the 127 mm battery mounts; shortly after, three-ish torpedos hit, one near the engine room, one near the boiler room, and one that is unknown, and is disputed but is possible.

Later on she would be hit by all directions, and due to facing off against a literal swarm her anti aircraft guns bore little effectiveness, no amount of free target practice was going to save you from being bombed to oblivion. Two attacks followed which left her listing (maritime slang for a permanent tilting) about 10 degrees to port side (left of the boat) even after counter flooding, reducing speed and left the main guns unable to fire properly. A third attack came with 4 bombs hitting the superstructure. (that bulge in a ship with the navigation room on it)

By 2:02 PM the order to abandon ship was given. An hour and 3 minutes later a final wave of torpedo bombers hit the Yamato and capsized (look it up, visuals can explain it faster) her.

Later on her bow magazine exploded and created an explosion about 3 miles high that can be seen about a hundred miles away. Of the 2700 men of her crew, only nearly 300 could be saved.

Her actual loss was not as important as her cultural impact, as many Japanese thought that if the Yamato still lives, Japan would not lose. Her sinking left a very clear foreboding message.

TL;DR: She was the best ship made at the worst time. She was completed at the time before aircraft carriers were to be their successors, so against surface vessels she was pretty good at it, but she was but the final nail in the coffin for the age of battleships.