The king indeed is not a weak piece, and in an endgame it's sometimes said that an active king is as strong as a rook. It's well known that in an endgame (at least where mating attacks are unlikely to happen) activating the king is one of the basic strategical ideas.
King as Offensive Piece

The king indeed is not a weak piece, and in an endgame it's sometimes said that an active king is as strong as a rook. It's well known that in an endgame (at least where mating attacks are unlikely to happen) activating the king is one of the basic strategical ideas.
Yup. But once a promotion happens, you should tuck your king away, is my opinion.

The king indeed is not a weak piece, and in an endgame it's sometimes said that an active king is as strong as a rook. It's well known that in an endgame (at least where mating attacks are unlikely to happen) activating the king is one of the basic strategical ideas.
Yup. But once a promotion happens, you should tuck your king away, is my opinion.
It all depends on the position and situation. Normally, in the endgame with fewer pieces, it might be considered a waste of time when your other pieces can protect it.

In my last game that I finished a week or so ago, my opponent and I were evenly matched until I activated my king, after which I dealt out a crushing defeat because he failed to do the same. Our material was nearly even the whole time (I had one extra pawn most of the game due to my opponent's gambit), until the very moment that my opponent resigned in a hopeless position, while both players still had a rook. It seemed that my centralized king was more powerful than either of the rooks...

The most important things in an endgame is:
1) Most of the pieces have been exchanged.
2) You are probably trying to promote a pawn.
3) Kings can indeed be attacking pieces.

Normally the King hides til the endgame, but there are (of course) some exceptions, like this game from GM Short. He needed an extra piece to attack and decided to get his king into the battle, with a decisive effect:
Recently, I've begun to notice little things like how vulnerable Rooks are to any piece which can attack diagonally(if this is something I was supposed to have done long ago, bear with me, I'm a chess beginner).
Now, Kings can move diagonally. In a chess game with a friend a few hours ago, the guy checked me with a Rook, and I promptly moved my King. He moved his Rook and I moved my King diagonally, eliminating it.
Aside from the fact that it was a major blunder on his part, I realised that the King isn't only a "pawn shepherd" but can also be used offensively in some situations.
Thoughts?