In SoCal we can grow Pointsettias in the ground. Usually it is older plants. I have tried to overwinter the newest hybrids and they most often die. Pruning them keeps them from getting too enormous. My friend Alice told me a good way to remember when to prune them; St. Patricks Day and Fourth Of July. I pruned a huge one in one of my clients yards today. It is an old double flowered variety called "Top Hat". The first pic is today's whacking(I probably should have pruned harder). The other is what the flower looks like November - February.