I have a MacBook Air running El Capitan, which is what it came with. I know that there is now Sierra. I decided, based on no real knowledge, that I should stick with El Capitan because that is what the machine came with. And I am additionally reluctant to switch since I bought a copy of El Capitan, The Missing Manual, for big bucks (although I admit to not using it). Just discovered that a new update to Numbers is now available, but cannot be downloaded unless I switch to Sierra. Would love to hear pros and cons on switching from El Capitan to Sierra, and whether the upgrade to Numbers if worth the effort. Thanks!!