Quote:By being aware of your practical playing strength, you can more easily identify your strengths and weaknesses, and also learn which areas of your game need the most work.
Hmm..
If I lose a rook endgame I think I should work on rook endgames. - Not necessarily, if you reached a lost rook endgame as a result of a tactical/strategic error. But if the player in question had a draw or win at some point, then I agree. But your rating should be used as a guide (along with the game, books and prior knowledge) to how detailed your knowledge of rook endings should be at your level.
For a 1200 player, knowing Lucena and Phillidor should be sufficient knowledge; for an 1800 player, knowledge of all the key Rook+Pawn vs. Rook endings is essential, whereas for a 2200 player it is also important to study positions with pawns on both sides of the board. The rating is used as one of several guidelines to find what aspects of Rook Endgames are most beneficial to learn.
If I lose by opening preparation of my opponent I think I should work on this specific variation. - Again, this is not always true; if you are uncomfortable playing the variation, you may be wiser to discard it from your repertoire and replace it.
Here considering your rating tells you approximately how much detail you should delve into in your study the variation. Below 2000 it isn't necessary to know all the theory on a line (a well-written book should be sufficient, or playing through some high-level games). Between 2000 and 2200 it isn't necessary, but it helps, and above 2200, it is very important to analyse games in the variation and record your analysis. Finally, above 2500, it is very useful to prepare novelties or little-known ideas to try out.
If I lose due to a tactical error I should work on improving my tactial abilities. - Correct. If you don't take into consideration your rating, then you may try to work through tactics books that are too basic or advanced. For example, if you are rated 1400, trying to solve the tactics in Informant will not be as beneficial as solving some puzzles on CT-ART. And for a 2450 player, solving the Informant puzzles and endgame studies will improve their play more than CT-ART, even though CT-ART is a very useful tool for sharpening one's tactical eye just before a tournament. For a player rated 2000, solving CT-ART will be more useful than solving Reinfeld's 1001 Brilliant Ways to Checkmate.
If I lose due to a bad strategical decision I should work on improving my understanding of positions. - Agreed. I admit that for this particular cause of defeat, rating does not play much role at all, except for deciding whether you should study a general book on middlegames/strategy or study the types of positions using a database.
If I lose because I am nervous... - Whilst your own rating is not relevant to this, your opponent's rating could be.
If I lose because of time trouble... - Write down the clock times for each move of the game. Here I agree with you, ratings do not have much relevance to this aspect of the game.
The rating does not tell me on which area of the game I have to work, only my failures show me. In extreme one may have an understanding of a master but perform like a woodpusher because he always gets in time trouble. I think you misinterpreted my post. 'Practical playing strength' does refer to rating, but it also refers to each individual aspect of your game as a collective whole. I did not say (or intend to say) that the rating tells you which area of the game to work on; I said that it is
a guideline (not 'the only guideline').
Just in case I made a grammatical error in my previous post, I will be more explicit: If you are aware of your practical playing strength, then by using your rating to compare the level of each aspect of your game with other players around your level, you can more easily identify your strengths and weaknesses.
Ratings also make it easier to learn which areas of your game require the most work, as at different levels there are certain aspects of the game that play a more important role than others. At club level, tactics play the most important role in a game, whereas at 2700 level, openings are one of the most important aspects of the game as the quality of play is generally very high.
If you need to work on ideas - good.If you need to work on theory - good.If you need to work on endgames - good.....
But how and how much should you work on them, and what aspect of the theme should be the focus of your study? This is where the rating should be taken into account.
Taking endgames as an example: If you are rated 1300, it is almost as important to study pawn endings as it is to study rook endings because of the difficulty of pawn endings and the themes which are common to several types of endgames, whereas at 2000 level studying Rook+2 Pawns vs. Rook with 0-1 Pawns is more beneficial than studying Rook vs. Pawns, as Rook Endings occur much more frequently than Rook vs. Pawns endings. But at 2200 level, it is important to know both types of endings, because of the tricky nature of Rook vs. Pawns endings.
But it all depends on the individuum (on "you") and not on a certain rating level. I find this comment paradoxical. It does all depend on the individuum, but their rating level is a feature of them, and therefore if the rating level was a completely irrelevant factor, then the individuum would not be an entirely relevant factor.
"You can more easily identify your strengths and weaknesses, and also learn which areas of your game need the most work."-
not the rating tells you but the game, the post-mortem and your conclusions