If your saddle slips while jumping, IMO you should use one.
Personally, I love the look of a breastplate. I use one when I jump my speed bump level jumps. I also use one when trail riding because I have one with LED lights on it and it makes us very visible and lights our way a little bit.
My horse bloats like a b. So a breastplate is crucial for me. I know its saved me from the dirt quite a few times. I think its also important for starting riders as a confidence boost while they are gaining their balance still. All lot of riders around here don't use breast plates for English. But I'm sure its flashy. I vote yes. Posted via Mobile Device
I ride in a 3 point. My next big purchase will be a much more appropriate 5 point. My horse jumps pretty hard and the saddle tends to slip. While I like the way they look, it is of the most importance that they fit well and that you're not just using a breast plate as an answer to an ill fitting saddle. Which I see a lot of on the jumper circuit!
I like using one on xc when doing banks and water and they might be taking some leaps. Other than that, if your saddle fits you shouldnt need one. I personally don't use a breastplate with elastic, because I've seen them snap before and it is not a pretty sight.