You scuff up existing paint for two reasons. First, you want to get rid of any oil, grease or dirt trapped in the top layer of paint. This is the stuff that cleaners and degreasers can't get off. The second reason to scuff is to set up a physical bond for the new primer and paint to adhere to. You want to give the old paint some tooth so the new sticks better.
Matt - Describes paints that give a flat, non-reflective finish. It is ideal for walls and ceilings that are not perfectly smooth.
Airless Tip: If you have somebody who can start masking off the trim, have them start on that while you convert the airless to a new color. When changing colors with an airless paint sprayer it is a good idea to have a second bucket filled half way with clean water. Place the intake hose in the clean water gently without getting the old color everywhere in the water. Take the tip out of the airless and spray all of the old paint out of the hose and back into its original paint bucket. Be careful when doing this that you recognize when the paint starts turning watery. When it does point the gun into the first bucket and spray until it looks pretty clean. It doesn't need to be perfectly clean. When it looks good, clean off the intake line in the clean bucket and get the old color off the intake line. Now place the intake line inside of your new trim paint.
Purple is the most contradicting color, to start at least because it consists of two antagonists: hot red and cold blue, ice and fire. It is the most mysterious color. It was the last color to emerge in art. Purple has a lot of other shades that are less rich and more lightened and muted: starting from light-lilac and going up to ashy gray-purple, which can give the interior a certain style and exquisiteness.
Step four: the key to a finished looking painting is to build it just like a house...and by that I mean layers. Paint it in the reverse order in which the eye sees it to make it three-dimensional. By this I mean paint what's farthest from the eye first, and build layer upon layer towards the eye. In other words, do the background first because it should be the farthest from the eye, then add the objects on top of that, and then add the shadows to complete the look. Ultimately it's common sense. If you paint a bowl of fruit, the bowl and fruit need to sit on top of that background, much as it would in real life.
The reality is that the guys shooting paint, even at the cheapest shops, know how to do it. They spray a dozen cars a week and have plenty of practice laying down smooth, consistent coats of paint. They work quickly and efficiently because they have to or they don't make money. They don't really make their money on shooting paint. They profit from body work because it takes time and insurance work because it pays well.
Since the trim is the first to go, the main body of the home will be shortly behind requiring painting. If the trim was recently painted, and a few years later the body is ready for paint, all the trim will need to be covered, commonly referred to as masking off. Masking off expends time, labor and material, which adds to the bottom line cost to the remaining 40%, typically costing an additional 25% for masking trim. Thus costing 25% more after both trim and body portions are painted in separate years.