I've played a fair bit of cribbage, but I've never heard of scoring one point for "Go" (as mentioned in this other question: Cribbage score going out). What is it, and what impact does it have on the game?
"Go" is when the count is less than 31 and the player whose turn it is to play has no legal plays (all cards remaining would put the count over 31). That player says "Go", the other person scores one point, and then plays any remaining cards in their hand (without going over 31).
The explanation at cribbage.org from rule 1.5.e.2 ...
- Players alternately play (place face up on the table) one card at a time, starting with the pone. The cumulative value of the cards played is announced as each card is played.
- When a player cannot play a card without the cumulative total exceeding 31, that player calls "go", and the opponent continues to play all cards possible (not exceeding a 31-count). The player who calls "go" plays first in the following 31-count sequence.
- Points are scored during this play of the cards (see scoring chart in rule 1.7).
Scoring occurs normally on these cards – points for pairs, runs, etc. are still scored – except that if such play takes the count to 31, that player scores an additional point: you get two for reaching 31 or one for Go, but not both.
The impact is generally small. It's unlikely that you'd get much more than two points during this time, as it takes at least two cards from your hand to reach a state where the other person would call Go, leaving you only two to play. You might be able to score a triple, but more likely you'd just get two or maybe four (with a pair) ... and your opponent might get those points back if you end up playing your remaining cards, e.g. by having 4-5-6 and being able to play them consecutively (after you've played your last card following Go).
You get 1 point if your opponent cannot "go" because the count is too high
The official rules of cribbage describe the general turn order of a cribbage hand.
During the count phase, each player lays down a card in turn, adding to a monotonically increasing score. Upon their turn, if a player does not have a card in their hand that they can play without taking the cumulative count past 31 then they say go, and the other player gets to peg one point.
That other player then continues to lay down cards until they also cannot play, until they are out of cards, or until they reach the exact count of 31. Playing your last card and hitting 31 exactly are each worth 1 additional point each.
This site has some good examples of how to score "go", which is probably the most complicated rule in cribbage.
How it impacts the game...
The obvious impact on the game is just another way to get a point. Practically, it influences what cards people play as they approach 31:
People tend to save smaller value cards for later in the count (both so they won't have to say go and to increase their chances of getting 31 and/or last card).
The sneakiest way to use "go" to your advantage is when you have pairs or runs of small-value cards near the end and your opponent has high-value cards. Once your opponent calls "go" you get to play your cards one-after-another until you also cannot go. Well if they call "go" at a count of 25 because 10-5-Q were played and they're holding two cards of rank 7 or above while you're holding three 2s, then you're in good shape:
You'd play 2-2-2, scoring 4 for the pair, 6 for the pair royal, and 2 for 31. At this point the count would start over, and your opponent would play their last two cards (hopefully not a pair).
More experienced players will also try and infer what cards another player has by what they lay down so that on their turn they can avoid playing into a count where their opponent could use their likely last card to hit 31 (or close to it). For example,
- If my opponent's penultimate card was a low-value card like a 4 and they'd previously played another 4, then I suspect they have a third one as well and I will try and avoid making the count 27
- I'll try and look at what cards they've played and what cards would complement them in terms of making runs or totals of 15 (or pairs, as described above), and assume they might be holding those cards
In practice, there are lots of things to consider during the count, and since go is only worth 1 point these considerations shouldn't weight as heavily as avoiding playing into a large run or a pair royal, but absent those circumstances, go considerations can influence your play.