It does make sense to put some sort of edging in place when building a pad for standing on. Edging will hold fill together. You fill right to the top of edges with a bit extra in the center. This fill will settle over time. So you may need to add more fill in time. You do not want horses brushing the pad edges with hooves or shoes to break it down. Many people here on COTH have posted their pads with board edges, built outside their runout stalls. Pad edges kept fill better contained as horses went in and out the outside stall door. They were using limestone fill in most cases.
We did not edge with the field driveway going thru the barnyard. Husband crowned it slightly for drainage, so the edges were short, not much of a step-up. He did scrape it down to hard dirt before putting down the fabric and crushed concrete. Being so heavy crushed cement stayed in place, not much moving in horse hooves. Fabric is a lot cheaper than the various grid pieces you can buy to cover muddy places. Still need to lay them on hard dirt to get them level, edges matching, before covering them for best results. Fabric needs a deep layer of fill on top, to keep it well covered.
Handy consumer idea is to ALWAYS buy the dirt/rocks in completely FULL truckloads, even if you may not need that much right now. Just pile the extra over out of the way to store it. Then you have it handy when needed later. Trucking cost is the painful expense when buying any dirt or fill. Pretty sure they charge delivery cost the same buying 40yards as they do 20yards. So get as much as possible in the truck when buying. Only pay one delivery charge.
You may not have thought of a use for that extra dirt or stone YET, but you will!. Ha ha