Note taking can be a fairly valuable tool if used properly. For the most part, it's better to take notes than not, although you can play very well without them.
Note taking isn't just a matter of just writing down anything and everything you observe, and if you aren't selective enough here you can end up with way too many notes, meaning too much quantity, and nowhere near enough quality.
I probably take a lot less notes than the average note taking poker player, and it's certainly because I really don't want to clutter things up with a bunch of stuff that I don't need.
I already have my poker stats on a given player and that will already tell me a lot about him or her. So I will make some notations but only in cases where I feel I can enhance the information I already have.
Good and bad note taking
A big mistake I see a lot of players making, even some otherwise pretty good players, is to take notes on specifics that are much better dealt with by looking at stats. So for instance you see someone check raising a certain hand and you note what he had.
We already have stats on this move though and from those we can get a much better idea of how a player uses a check raise besides noting a few instances of it. So just going with this one or couple of instances can actually end up doing more harm than good, just like putting too much weight on a small sample of stats would.
Our notes should instead be looking to tell a story about a player, and not just any story but one that provides information that can only be gained by observation and not tracking. If I can get a certain type of information from my stats, well that's what they are for, and I'm not going to be able to track that stuff better than the program that I have to do it, and in fact I will do an inferior job at it.
What to take notes about
However, there are some things that I just won't be able to track very well, such as for instance how a player adjusts to certain moves put on him, how he or she plays in certain other types of situations such as late in a sit and go tournament, and so on.
So whenever I am looking to make a note on someone I always ask myself if this is really adding to my knowledge of this player and if the information is something I can use later. If the answer is no, I don't bother with it.
For instance if a player likes to three bet pre-flop, I don't really need to know or care what they are doing it with, whereas a lot of players would make notes such as three bet air pre flop and so on. From the amount of times he or she does this, the frequency in other words, I can get a much better feel of what they are doing.
Note taking really isn't or shouldn't be a substitute for interpreting player frequencies, although not a lot of players have all that good of an idea how to do this properly. However, that's what I would focus on first, and then looking to add good notes to augment this knowledge, not substitute for it.
If you don't take the right approach here, you can get in a situation where you're reading a whole bunch of stuff when you look at the notes on someone, with a lot of the stuff statistically insignificant and some of it even contradictory.
So learning to take good notes is like everything else in poker, where you start out at a certain point and then look to improve things as you gain more experience. If you are newer to this, then I'd suggest that you not be shy about taking as many notes as you feel you should, however as you go along you should look to always question the value of certain notations.
Then, as you progress, you will find that you end up taking less and less notes and the notes you do take will be more and more helpful, which is what good note taking is all about.
If you want to learn more about note taking, ask Maria Ho, a gorgeous poker pro.