Creates a much deeper level of connection and brings your reader closer to you/your characters. It creates empathy and invests the reader.
Allows the reader to feel what the character is feeling. So your reader feels and sees the thing you want them to see. Rather than just stating facts.
Describing the senses makes it more real as anyone can connect to it.
TELL: the boy was sad
SHOW: His chest tightened as his eyes formed salty rivers draining off his face. Sniffing repeatedly through his scrunched nose uncontrollably dripping with emotion. Clouded thoughts provoking a fearful tremor, shaking the tears off his chin.
TELL: the dog wanted to go for a walk
SHOW: Rushing back and forth, accelerated by excited panting as slobber flew out the corners of her hinged open jaw. Staining my floor with a pungent meaty stench from last nights dinner. Paws millimetres from the door as she urges to escape the barrier in which we call the front door. Eyes bewildered by vast outdoors with endless running around space.
TELL: When they embraced she could tell he had been smoking and was scared.
SHOW: Immediately deterring me from him as the piercing ashy smell of cigarettes seeped into my own lungs. A stench so thick that if I were to get any closer it could invade my tastebuds with a horrible flavour. Twitching tremor filled my hands which I disclosed from him quickly to hide my fear.
TELL: The temperature fell and the ice reflected the sun.
SHOW: Chills felt my body up and down, triggering shivery bumps everywhere the cold touched.