Historically, I believe, they did only use them if the lady was a frequent rider and of at least sophisticatedly wealthy standing...if you know what I mean. * laughs a bit * If they were a frequent rider and of that standing, that usually meant that they had carriages if they actually wanted to go somewhere, so they rode for exercise or sport or air or whatever they did things like that for, not really to get somewhere specific.... Sorry, I'm trying not to sound like I know a lot, 'cause I don't.

I haven't studied it, only seen it portrayed, so my details are a bit vague.
No reason, I just mentioned that that was something that you could change easily depending on the circumstances and characters in your story.
