If the reply is only going to be a sentence or two, I just use the answer box. If its going to be more than a paragraph, I usually compose my narrative in a word processor, seperate from the browser, complete with link codes and everything. That way I don't have to worry about the accidental page change. Also I can save it and come back a bit later to continue. When finished I just copy and paste into a Wikitree answer box.
In my case, its largely because of my declining eyesight and arthritic fingers. Using Notepad or wordpad gives me a chance to try to catch most of the typos and misspells. Usually, but not always.