Hello. During a recent game, my opponent commented that I was ‘filling in my points’ and later stated that I was giving them ‘prisoner points.’ What do these things mean, and why are they disadvantageous?
Under Japanese rules (which are default here)
Only empty intersections that are surrounded by stones of your color count for points.
Thus, in the example below both white and black have 6 points for territory.
If white got scared for some reason and played another move to make sure all the stones are safe…
White would now have only 5 points (remember that only empty surrounded spaces count)
Hence filling your own territory (if you do not have to) is disadvantageous.
As to prisoners, in Japanese rules a prisoner is worth 1 point. If you play inside your opponent’s territory in such a way that your opponent does not need to respond to that move, you just gave him an extra point. If your opponent DOES have to respond than he would fill his own territory and thus there would be no change (+1-1). Hence you should only play into your opponent’s territory when you think he/she will respond or that you will be able to survive there with your stones (form two eyes).
Some basic learning resources:
and a very old, but very thorough guide:
http://www.playgo.to/iwtg/en/
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Excellent - thank you!
You should pop that example into the doc somewhere 
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