The idea for accuracy is consistancy, each loading procedure needs to be the same.
Each time BP (or sups) is shot, the burning powder leaves a residue in the barrel stuck along the sides of the bore.
aka; fouling.
If nothing is done, this material will buildup every shot causing a constricked bore and change the pressure. It's not so much as to make the gun unsafe to shoot, but it will get tougher to load and the slightly different pressure affecting your projectile will change it's flight and point of impact, believe it or not a fouled bore will lower the group.
You can't eliminate fouling but, there are plenty of way's to eliviate fouling build up, I'll not argue the ways, I'll just tell ya what I do.
I'm a swabber, that means I swab the bore after each shot, every shot. I count on taking a preliminary "fouling shot" before I begin in any compitition. Hunting is different, but I still do hunt with a bore that IS NOT fully clean.
All of my guns have a perminant cleaning jag attached the the carry ramrod, I use it for seating and cleaning and don't have to worry about finding one to screw in,,it's there. I use 100% cotton .22 cal cleaning patches, there cheap for the bag count, and they are all cut the same size and thickness. Make a shot, take one 22 patch, pop it in my mouth and saturate it with spit, press it out a bit with tounge and roof of mouth, take that damp (not wet) patch and push it once all the way down and all the way back,,no scrubbing motion, just down and back. Toss it, load, shoot, repeat.
others milage may very.