Sometimes, especially when a thread has a lot of replies and you want to answer one that's not the last one, it makes sense to quote that post so others will know what you're referring to. To make for easier reading, you can delete everything except what pertains to your answer.

There's a little trick to that. When you answer a post,  click "quote" in the gray shaded box, but you can't delete parts of it until you've typed in an answer. Then you can go to the quote and delete parts of it or shorten what sometimes seems to be a very large blank space at the end.