For the most part, yes, they are a great guide to see if a plant will work in your landscape…… although, keep in mind that when looking at potential size, it can sometimes be deceiving.
As an example, some shrubs give a 10 year estimated size. If you use the 10 year size to locate your plant but you plan on having the plant stay there forever, the actual potential of growth could be much larger….even double the 10 year size. This is something to consider when siting your plants.
Also, don’t always assume that a dwarf plant won’t get very big. ‘Compacta’ burning bush can reach 10′ high and 10′ wide, but you still see them planted under a window against the foundation, and people just prune them into hedges. A plant looks best when allowed to take on its natural form.
Keep these things in mind when looking at the tag to determine where you will site your plants. Use other resources as well to check on potential size so that you make the best decision for your plant and your landscape.