The question in the title can be answered very simply. Some surfaces shouldn’t be painted with a roller, or even a brush, for there is always the chance of leaving marks and ridges. You can make the decision up to a point, based on saving time, but that shouldn’t be the major factor in helping you make a choice. Efficiency is part of the puzzle, but you should pay more attention to the job you’re trying to do and the finish you’re trying to achieve.
Use a roller for large surfaces, such as continuous walls with little or no breaks or objects to stop you. Using a roller can reduce the amount of labor quite a bit. Naturally, a sprayer can give you the same time-saving/labor-saving results. However, you have to consider conditions, such as air movement, in which you’ll be painting. It’s also important to think about how you’ll replenish your paint supply in terms of pouring fresh paint into a roller tray or refilling a container.
Type of Paint
When trying to decide between a roller and a sprayer, consider the type of paint you’ll use to get the results you want. If you’re painting walls and floors, you may want to use a roller to maintain the density you’ll need. This should work best in industrial and large commercial settings. Use a long-pile roller for rough surfaces, and a foam roller for a smooth surface.
Spraying the paint on similar surfaces can work too, though you may want to practice a bit in an out-of-the-way place. It does take a certain touch to get a consistent finish with spray paint. When choosing spray, you should also give some thought to high volume-low pressure for furniture, stairs, window frames, and cabinets. The opposite, high pressure-low volume spray would be better for vast areas and long-distance reach.
Rollers can be a good choice for putting paint on those large, flat areas in a short amount of time. Someone who has a bit of experience may find they can cover the same area in a similar amount of time with spray, but it’s necessary to pay close attention to the thickness/coverage when spraying. If you get this part right, you may be able to save a lot of time, especially if you need a second roller coat to get consistent coverage.
Type of Surface
The type of surface (rough, semi-rough, smooth) has been mentioned, along with the suggestion of using the right type of roller for each. Of course, if you’re painting a rough, ridged surface, you may want to select the spray method. Your finish could be much more “even” or consistent, especially if you have a good touch with the sprayer. You’ll also find that using a paint roller can be more tiring since it requires a bit more physical activity.
Newer spray paint equipment is light and rather easy to control. Some people will do just fine with one hand, so you can switch hands when necessary. You’ll also be more efficient when painting in areas that have nooks and crannies. The spray equipment should reach into those very well. If you do the larger surfaces with a roller, you’ll have to go to in with a small brush to get a complete job.