This

is one of my favourite examples of why you should leave covers intact.
Off paper, the used Queen Victoria Indian ˝ Anna stamp is worthless. They were printed by the billions.
Cut to shape, to retain the postmark, you might get 20c for the nice strike of the Jammu postmark.
Left intact, it's a tens of dollars item. First up, it's a mourning cover, with the black edging to the envelope. They were used, particularly in the 19th Century, to announce deaths and send condolence letters. There are a number of collectors who specialise in them.
Then, there's the historical interest of the recipient. Lady Younghusband was the wife of Colonel Sir Francis Younghusband, who led the 1904 British Expedition to Tibet. If you're old enough to have read Rudyard Kipling's
Kim about the Great Game in Central Asia, Younghusband was a key player in the Game. The British Residency in Srinagar, the Summer capital of Jammu & Kashmir, was also one of the key centres of the Game.
Finally, there's the fascination of the route the letter must have taken, from Jammu in the lowlands of Jammu & Kashmir, over the mountain passes and down into Srinagar. And as this letter was sent during the Indian Winter (which was very hard at Srinagar), it must have been a very trying trip for the postal runner who would have carried it.
Trim this cover down to its stamp, and you lose not only a lot of money, but a delightful historical artefact.