Cubing butter before refrigeration is not necessary, but it can speed up the softening process later, making it more convenient for baking.
The primary reason to cube butter before refrigeration is to increase its surface area. This allows the butter to soften more quickly and evenly when you take it out of the refrigerator to use in your baking recipes. Softened butter is crucial for many baking recipes as it allows for proper creaming with sugar, which incorporates air and creates a light and fluffy texture in the final product. If you often forget to take butter out in advance, cubing it beforehand can be a helpful time-saver. However, if you have ample time to let a whole stick of butter soften at room temperature, cubing it beforehand is not essential. The softening time will depend on the ambient temperature of your kitchen.
If you need softened butter quickly and didn't cube it beforehand, try grating the cold butter with a cheese grater. This creates small pieces that will soften much faster than a whole stick or even cubes.