I've been using my OS X system since +-2012. I started with an MacBook Air and migrated everything to a new iMac early 2013 (late 2012 slim version). Late 2013 I replaced the internal harddisk with a 1 TB SSD and migrated the whole system without any flaws. So, my OS X has been running for several years all together. But it isn't very stable anymore. Sometimes it freezes and I have to wait several seconds to get back to work. It's much slower than it used to be. Also certain mouse clicks aren't registered anymore, especially when I want to close a tab or a program. I have to click next to it and then on it again, to get it to work. It's not impossible to use, but annoying. I must say I'm a heavy user and I use my iMac daily for work, sometimes more than 12 hours during a day. It's a 27" late 2012 iMac with 3,4 GHz i7, 24 GB RAM, Geforce 680MX (2 GB) and a 1 TB SSD. Apart from that I'm using a 6 TB Thunderbolt drive (2x6TB, RAID1), with a lot of photos and videos. I have a 1 TB Time Machine-drive attached via Thunderbolt as well. I use a ton of programs, including Adobe's Creative Cloud apps (PS, LR, ID), MS Office, a large music collection in iTunes, Apple Mail with 10 email-accounts and a couple of games (Xcom, StarCraft, ARK). OS X is still workable, but I think it could be much faster and more flawless. I guess I installed too many programs during the years. I already tried to reinstall OS X El Capitan but that didn't make a difference. I'm now considering to start from scratch, with a clean OS X install. So formatting the drive and use it as if it's brand new. And then to install my software, email, music, etc one by one. This is a major operation to me, especially because I have so much software installed (and music, photos, videos, games, etc) and I need the computer for work. I do have a MacBoor Air as a backup though. I'm interested to get some feedback from you guys. Did you ever start from scratch? And how much fuss was it to reinstall all your user data? Did it perform better afterwards? Or do you have some advise to restore my current system without starting with an empty OS X from scratch?