When new GM Matt Klentak traded away Ken Giles to the Houston Astros for a major package that included former #1 overall MLB Draft prospect pitcher Mark Appel, they traded their ‘Established Closer’ (trademark pending.)
Having a proven closer to lock down the end of a game is usually considered a luxury that a rebuilding team doesn’t need, because saves are expensive and there is little need in having money tied up in a closer. Giles was inexpensive, but that also helped place him at the very peak of his trade value.