Background on this question: I have a litte server with five HDDs pooled together in a RAIDZ. Last week one of my HDDs died. So I bought a new HDD and replaced the dead HDD. During the resilvering the inevitable happend - another HDD died but thanks to ZFS I could recover most of my data (Thanks to all my friends for supplying external disks).
Now as I'm replacing the second HDD and need to destroy my old pool I'm thinking about creating a degraded RAIDZ2 with my five HDDs for adding a sixth HDD later. Why could this be a bad idea.