Extremely important to protect your king. It also releases a rook.
The only reason not to castle is for the tempo to try and attack your opponent before he attacks you. But it is much easier to attack a king in the centre then a castled king. I try to castle kingside when no pieces are under attack at the first opportunity
Until you can accurately tell when you should castle, just castle as early as possible.
You should not castle when you see the enemy pieces or pawns pointing at the side of the board you were going to castle to.
If you're the sort of person who flips a coin to decide what to do, that's even better, because there's only a 50% chance you'll be wrong.
If the center is closed and there is no realistic chance of the enemy launching a successful attack, use the tempi (plural for tempo) to do other things instead of castling.
You should probably catle when the center is open (few or no pawns in the center, or the enemy is ahead in development and is aiming at the center.
Uhm...to stereotype castling or not castling is a HUGE error. It depends on the opening played. Some involve immediate castling to one side or the other, like the King's Indian Defense, where the Black King always castles Kingside quickly. However, in say, the KIA vs Sicilian (1.e4 c5 2.Nf3 Nc6 3.d3 g6 4.g3 Bg7 5.Bg2 e6 6.O-O Nge7 7.Nbd2 d6 8.Re1), the move 8...O-O is a mistake as Black commits his king too early and White has a fixed target on g8.
Castling is an option, not an obligation. It's just that it has a high success level (80+%), but there are still times when it's available, but a mistake.
It is much easier to attack a king unguarded in the center of the board, than to attack the king when it is secure behind a strong pawn formation on the edge of the board.. plus it also develops the rook in the centre. There are exceptions when you won't need to castle, but usually as a rule, is better to castle early to develop all your pieces into the centre, whether it be castling short or long.
The king belongs in the center of the action where he can ghet to the otheir side man.
..right between the queen and another piece
It is easy to attack a king that is in the middle if the position is open. (and it can be opened up usually) And the other reason for castling is that you need to activate the other rook. If you do not move the king, your rook remains passive. In closed positions, or positions without queen you may play something like Ke7 to connect your rooks, but usually you need to castle to activate the rook.
It's still not that simple. Trade enough pieces early on, especially the Queens, and castling could be a really bad thing. If White's King is on g1, and Black's is on d7, you are in a Rook, Minor Piece, or Pawn ending, assuming all other factors are equal, like neither side has a protected passer or a material advantage, Black's probably better because his King is better prepared for an endgame, in the center and up a rank.
I have put this post in the forum 'Chess Openings' as, just about always, castling occurs in the opening stages of the game once specific pieces have been moved out of the way, pawns, knights, bishops..
However, what are the actual benefits to castling? Personally, I don't like the idea of leaving my king locked in a corner of the chessboard. Howeve, most games that I have seen of professional chess players, both on chess.com and on international matches castle. Why?
When should I castle? Why should I castle, or, perhaps, when should I not castle?
Thanks in advance