Actually, for beginners, I think it’s a good idea to encourage that they fill in dame, for the sake of understanding some potential complications that can arise. Often there will exist consequential dame that do affect the score (by requiring a reinforcing move). I think that beginners should not be told to take shortcuts, since then it might prevent them from learning some endgame intricacies. Hence, stronger players should also show some patience when dealing with a beginner or weaker player, since their opponent might not see all of the implications or understand that some things are settled, and anyways, the practice of playing some things out might offer a learning opportunity.
On the opposite end of the spectrum, I believe professional players routinely fill in the dame when playing out a game to the scoring phase. It’s really just the intermediate players in between that routinely skip dame filling in casual games, but taking such shortcuts requires a level of mutual understanding and agreement.
Here’s a simple example of a dame that “matters”.
Of course, White could fill A to force Black to defend at B, or maybe Black would preemptively fill at B (usually when there’s nothing else better to do) before A is filled. Yet, often people playing on OGS might leave both A and B unfilled, and instead pass, since OGS (and other servers) have a scoring feature to mark both A and B as “dame” (or neutral) that do not count for points. While all of this is obvious to intermediate level players, a beginner might not realize all of this. Some might leave both A and B unfilled, but then not realize that B should be marked as “dame” during scoring. Other beginners, playing as Black, might make the mistake of filling the dame at A first, or neglect to defend at B when White fills at A. Potentially making these types of mistakes (or at least presenting the opportunity to think about them) might be good learning opportunities for some beginners.
Here’s another similar example:
Here, a beginner might overlook that C is a crucial dame that both players should eventually (when there are no bigger moves left) want to play first, since one point (and possibly even the game) hangs in the balance. On a side note, an interesting quirk of the Japanese rules is that if both players passed while leaving the dame B and C unfilled, and the game was close enough (decided by a half-point margin that would flip depending on who gets to fill C first), then both players would lose!
Another type of dame filling learning opportunity can occur if the situation from the previous diagram appears in one part of the board, while the situation depicted below appears in another part, and imagine that the rest of the board is completely settled with no other remaining dame.
Here, if it was White’s turn to move, it would be important for them to not pass and to recognize that D should be played first (requiring a response from Black at E), which then lets them fill C as well (eventually requiring another response from black at B). Of course, White playing at C first would be a mistake, since that allows Black to then play at D, and ultimately allows Black to save a point (which could even cost the game).
All of these implications are of course obvious to intermediate players, but I think it’s valuable for beginners to have the opportunity to play out these type of situations in order to learn.
Some dame might have to be filled to ensure that scoring is properly done on OGS
Here are some other interesting dame filling examples to illustrate some potential limitations in the scoring phase to indicate dead stones and null territory.
I had a situation like this in one of my games.
I think it might be possible for both players to take a shortcut by passing in this situation, but then both of the marked White stones would need to be marked as dead, while 2 and 4 should be marked as “dame” (non-territory) for Black. In this case, the position of the dead (marked with X) White stones would also count as two points of territory.
However, consider another situation:
Here, I think taking a shortcut of passing might not work, since one would have to mark 2 as non-territory, X as dead (for counting as a prisoner for Black), but then the space under X as also non-territory for Black (since Black needs to connect there). I think that it might not be possible to mark the board in such a fashion on OGS during scoring.
However, in both of these two cases, a simple work-around to ensure that scoring is properly done is to play out the dame filling, in order to compel black to capture (and connect, in the latter case).