they're good moves because usually the knight controls a key square like e4,e5,d4,d5. if they did a d4 opening and then later did Nc3 pined the c3 knight then they can't do e4 and if they already have then it's more that likely undefended. also look out for traps like this when pining or being a victim of a pin.
well let's look at the position except black doesn't retreat.
these doubled pawns are a pain for white positionally. black's nearly equal. white actually shouldn't of done a3 but instead done either Bd2 or Ne2. i was demonstrating a trap here's an example of black winning from a pin.
when your typing a comment you see logos a the top of the comment typing area. the one with the 4x4 chess board on it is the one that'l let you insert a game.
In your last example White has 6 Qg4 winning back the pawn after either 6.. Nxc3 7 Qxg6 Rf8 8 bc or
6..Nf6 7Qxg7 Rg8 8 Qh6
most beginners won't see that move. they probably don't even know to do h4 if Ng5. in this specific example it works but sometimes you won't .
If the bishop has no other useful post or it's the "bad" bishop (you can google that chess term) then that can be a reason.
If you want to undermine the central square the knight is influencing then that can be another reason. (If the central square is defended by many pawns then removing the knight's defense with the pin may be pointless.)
If you want to induce a move like h3, which can be a weakness, that can be a reason.
So basically you look for the value of the knight and the value of the bishop. Not only what they're doing now, but what roles they might play in the future. For example your "good" bishop may not be doing much now, but in the future it will likely find a useful role due its relatively high mobility and at least defensively will be useful to cover the color complex your central pawns have abandoned.
In general they are good moves, but, of course, it depends on the game situation. For example in the Vienna Game or Bishop's Opening. White wants to get in an early f4 and launch an attack on f2, g2, and h2 so posting a Bishiop at c4 is a better idea than b5.
On the other hand, in some openings Black or White wants to get his Bad Bishop (the one blocked in by his own pawns) outside his Pawn Chain before he completes setting it up and pinning an enemy Knight or even exchanging with it is a much better plan than letting it sit unused and a prisoner of its own pawns.
(Black side)
Black Bishop B4 (pinning a C3 knight)
Or
White Bishop G4 (pinning a F3 knight)
Or
White side,
White Bishop Bishop B5 (C6 knight)
Or
Black bishop G5, F6 knight.
These moves attack a knight, pinning it to either the King or queen.
So would you say these moves are good moves? I think that Bb5 and Bb4 are particularly bad moves. And what is the best way to counter? Use the outside pawns, threatening to take the bishop if it doesn't take the knight, or a is a move like putting your bishop behind the knight a better idea?
Nice talking to you all, would love to hear your opinions.