So I'm running on out space on my macbook (250 gig ssd) and want to upgrade to El Capitan. But I don't want to upgrade what I have, since I'm sure there's tons of junk on that drive I don't want. So I'm making a new 35 gig partition to install El Capitan on. Then, I backup my the rest of my hard drive with time machine. The plan is once I'm happy with El Capitan, I'd delete the old Yosemite partition, since all the data is backed up in time machine anyway. But I'm not sure exactly how that's going to work. Once I delete the old partition, and give El Capitan the whole 250gigs, if I turn on time machine, it will want to delete everything on the backup drive first, right? Or will it recognize those backups from Yosemite, and want to use those? It's almost like once I back up Yosemite, I need to partition my backup drive to a Yosemite backup, and an El Capitan backup. Then just copy the few things I want from the yosemite backup manually to my hard drive, and set up the other half of the backup drive as a new time machine backup. Does any of that make sense? I feel like I'm missing something here, because it seems awfully convoluted.