Upgrading OSX from a combo update.

@jgwatson

With Apple updates, the combo updates only work when on the same major revision of OS X, e.g. the 10.10.3 combo will only update 10.10.0 - 10.10.2. There is a full version installer from the App Store that will upgrade 10.6.8 and later to 10.10.3 (provided the computer meets the requirements).

Must be 10.10.0 through 10.10.2 to use the 10.10.3 Combo Update.

To upgrade a Mac from an earlier OS, you need to use a full OS X installer, like the kind you may get from the Mac App Store as one example, not a Combo Update.

How Apple defines update versus upgrade
https://support.apple.com/en-us/HT201564

Another point to consider with Combos:
10.10.2 has been out a while, and when Apple released the last security update to it, it changed the build number. That change meant that you could not install the 10.10.2 Combo Updater over 10.10.2 like would normally be possible (you'd have to run it before the security update).

So, the general rule with Combo Updaters is that you can install them to upgrade any version prior to it, with the exception noted above and when you have a (as an example) 10.10.0 to 10.10.1. There would not be a Combo Updater for a .1 release since it's the first update.

10.10.3 Combo can update all 10.10.0, 10.10.1, 10.10.2 installs. That is in theory as I have not tested them all at this point. 10.10.3 Combo should also be able to be installed on 10.10.3 at this stage.

@boettchs actually brings up an interesting and important point on Combo updates. Combos are the only updaters that can be "re-installed" on top of the same OS version in most cases. For example, if a tech or user installs the 10.10.3 Delta updater on a Mac running 10.10.2, that delta updater can't be installed again on the same system while its still at 10.10.3. The Combo update will install again though, even though the Mac is already running that OS version.
Why is this important? In my experience, and I think others will agree, delta updates tend to be more flaky, and can introduce odd problems. Think of these updates as "surgical" updates, in that they only install the changes from one point release to the next. The Combo updates are more "holistic" since they include all changes from the X.X.1 release up to the current one, rolled together. They just tend to work better I've found.

Whenever we offer an OS X update in Self Service, unless its the initial .1 release which is always a delta as boettchs explained, we use the Combo Update. This ensures for one that everyone running some version of 10.10 will be able to install it, and also ensures a more reliable update experience.

I forgot another exception to the above. What's important to note is not only the OS iteration, but the build numbers. Sometimes a new Mac model comes out in between OS releases. In this case, special builds of say OS X 10.10.2 may be present on the new Macs. It is highly likely that the 10.10.2 Combo - released prior - will not work. Putting all this out there because if you're going to scope Self Service or other policies with OS X Combo Updates, you have to take those bits into consideration with scope.

As @mm2270 states, Combos have been used by many Mac admins as a stop-gap to doing a full OS install and may cure some issues with prior delta installs.