If you get a bit worried about jumping skinny fences on the XC, and perhaps a bit ‘hooky-looky’ rather than riding smoothly forward to them, this is a really good way to build up your confidence, and your horse’s, at skinny fences, hopefully without risking confidence-sapping run-outs.
A double, or a good related distance, will mean that you don’t have to worry about seeing an ideal spot, you can just ride forward between the fences and let the second one come to you. The jump stands help a bit with the straightness, and it really concentrates the mind and stops you from allowing the tiniest bit of drift on the approach.
These short poles are helpfully marked so you know exactly which bit to aim for, too.
The white poles are to either side in the first photo, and then as V-poles in the photo on the right, to encourage neatness in front and a better shape over the fence.
Of course once you are both confident and straight, you can swap the tall jump stands for barrels or short stands, to make them more like xc fences and increase the test.
I’d put flags on them at that point, to help the horse, training it to look for the flags.