Generally when you post within a topic, you add your opinion or comment to the thread.
You may quote a previous poster by all means. Quotes are a good way to help others put your reply in context especially if your reply is some way on from the point you are replying to.
There is no real need to quote the previous post if you are replying directly afterwards.
There is also no real need to include that whole post of the one you are referring to. You may edit the quote as such:
QUOTE (name of member being quoted)... I like blue trains ...
Use suspension points '...' to indicate that there was other content before and/or after the text being quoted.
What I assume some members are doing is using the Quote Reply button next to a post:
instead of the normal topic reply button. This button should be used when you specifically want to quote the text of the post next to the button.
The topic reply button:
that is found at the top and bottom of the topic is what you should click when making a normal post, replying to the thread.
Including whole posts and loads of images in quotes just makes the process of reading threads more difficult for others. Please press the right button.