It's all to do with pushing the counters nearer the edge, so if you play a counter and it pushes more counters near the edge then you run the risk of the next person getting their question right and playing their counter which may result in them pushing counters to the win zone, it was the most boring thing on telly until Take on the Twister started, that doesn't make any sense at all, hopefully The Chase will be back soon
Because in the first round they have 3 counters each, getting a question wrong loses a counter. If you pass, an opponent has to use their counter, so if you think it won't pay out, you don't waste your counter. Then you can answer another question because you have a counter left.
...if you answer a question right, why would you let someone else play instead of you? I understand that they can then move counters into a good position for you to then win some, but couldn't you also do that? If you answer a question right, and then play instead of passing, you don't run any risk of someone else winning counters by fluke that you could have won!!!