Game selection is very important in poker and this is especially true as the number of players decreases at a table. At a full table if there is one really bad player the benefits of his lack of skill will be shared by the entire table. At the other end of the spectrum is heads up play where 100% of the equity an opponent gives up will go straight to you.
Additionally, at a full table it will take more time to reap the benefits of playing against a bad player because everyone plays so many fewer hands with more people at a table, and thus there are fewer occasions when you and the bad player are in the pot together where you are earning money because of his mistakes. Of course, the opposite is true and if you are the inferior player in a heads‐up match you will lose your money faster. Therefore, especially in heads‐up play, it is important to find the good tables and to leave the bad ones alone.
Just how important this is, is obscured by the idea of win rates. Take the amount of money won and divide by hours played and this is your hourly rate. It is helpful information but it is an aggregate of other information, and thus misrepresents what really happened. It can be used productively, but must also be used carefully. This is because the notion of “hourly rate” makes it look like for every hour played the expected value was the stated amount, and that for any given hour in the future the same expected win rate holds true.