Yes, washing your hair before a haircut is generally recommended. Clean hair allows your stylist to see your natural hair texture, wave pattern, and how your hair naturally falls and behaves—all crucial information for cutting the right shape and length. Dirt and product buildup can make hair clump together unnaturally, preventing your stylist from assessing the true volume and texture.
However, there are nuances. Washing immediately before your appointment with wet hair isn't ideal; instead, wash your hair the night before or the morning of your appointment, giving it time to dry naturally. This way your hair has its natural oils restored (which protect your scalp during cutting) while still being clean. Some stylists actually prefer very lightly product-free hair for certain styles.
The main exception: if you have a very short cut or are just getting a trim, the exact cleanliness matters less. Similarly, if your stylist specifically requests you come with unwashed hair (some do prefer this for specific techniques), follow their guidance.
One practical tip: if you wash immediately before your cut, your newly trimmed ends will dry differently than they will in coming days. Waiting a few hours after washing lets you see more realistic final results. Communication with your stylist about their preference is always worthwhile—good stylists often have specific preferences based on their techniques and your hair type.