Professor Trelawney is somewhat notorious for her drinking habit. She often uses the Room of Requirement to try and dispose of her empty bottles.
Harry sprinted towards [the noise], his wand at the ready, hurdled round another corner and saw Professor Trelawney sprawled upon the floor, her head covered in one of her many shawls, several sherry bottles lying beside her, one broken.
"I - well," said Professor Trelawney, drawing her shawls around her defensively and staring down at him with her vastly magnified eyes. "I wished to - ah - deposit certain - um - personal items in the Room..." And she muttered something about "nasty accusations".
(Half-Blood Prince, Chapter 25, The Seer Overheard).
Yet there is a spell that specifically vanishes unwanted items.
"Bill took out his wand, muttered "Evanesco! and the scrolls vanished.
(Order of the Phoenix, Chapter 5, The Order of the Phoenix).
Why did she carry her bottles through the castle to the Room of Requirement when she could have simply vanished them by magic?