They are inaccurate because of the large meniscus. Graduated Cylinders: A graduated cylinder is a quick and easy (though less accurate) way to measure the volume of a liquid. Volumetric pipets are so accurate because the long neck decreases the error in measuring volume of the meniscus.
Just so, why would you use a volumetric flask instead of a graduated cylinder?
A graduated cylinder is just what its name implies. Cylinders are designed to contain an accurately known volume, but are usually used to dispense that volume. Therefore, they are not as accurate as a volumetric flasks, but the fact that they are graduated makes them more versatile than volumetric flasks.
What is the precision of a volumetric flask?
Volumetric Glassware. In quantitative chemistry, it is often necessary to make volume measurements with an error on the order of 0.1%, one part per thousand. This involves using glassware that can contain or deliver a volume known to a few hundredths of a milliliter, or about 0.01 mL.