Consider the photo of a model of USS Constitution below. It shows the main (right) and mizzen (left) masts. From bottom to top the mizzen mast consists of four parts, lower, topmast, topgallant, and (rarely) royal.
The topgallant and royal masts are the lightest, have the least support, and face the most stress from wind and motion per unit of area than any of the masts. When severe weather was expected, the royal and topgallant masts could be disconnected and lowered to the deck to prevent damage.
Removing weight from so high on the ship also improves the ship's general stability.
Raising and striking masts while underway is one of the most complex and physically difficult tasks that could be undertaken on a sailing ship. The ability to do so and doing it early enough might be critical to the safety of the ship in a storm.
I have been to the top of the mast on my ship while in port. The motion is considerable. I would not want to be up there while underway even in relatively calm seas.
I hope this answers your question.
SpyNavy
Garde la Foi, mes amis! Nous nous sommes les sauveurs de la République! Maintenant et Toujours!
(Keep the Faith, my friends! We are the saviors of the Republic! Now and Forever!)
LonePalm, le Républicain du verre cassé (The Broken Glass Republican)