If you meant the Windows 7/8/8.1 update, that's fair - such a large update SHOULD have some warning or be opt-in - I know that if I had that update on my previous install of Windows 7, it would have rendered my computer unusable WAY before it finished downloading - I had trouble keeping the free space over 4GB (I heard that you should have free space equivalent to your RAM to make sure you have swapspace) because of that WinSXS bullshit, and ONCE I used a program that filled that hard-drive 'till I had 200MB left, and my computer slowed to a crawl. (Context: the way my computer is configured, I have a ~50GB partition on my HDD for Windows, and I install everything else I can, which I found out includes Windows' documents folder which encompasses Music, Pictures, Downloads, Videos and Documents, on a secondary 1TB partition - that way, if the OS does something I don't like and is hard to get rid of, or I made a mistake and scrapped the OS, or something else, I can just call blank slate on the OS partition and start from scratch without losing other data or needing to reinstall my Steam library).

If Windows 10 itself is hard to remove when installed? See above comment - it's not an issue for me (and I urge anyone who can bother to do the same, it saves a LOT of time when reinstalling an OS)