Return to Revisions

Answering your 4 questions:

1. Differences

   1. Remote Event Receiver (RER) -
      1. A provider hosted app is must, which means you need additional infra. Apparently, as pointed out by Mihail-Florin Popa, it is no longer true.
      2. Works using web services, you expose web services on your provider hosted app, that are called when an event is fired.
      3. Only Client Object Model is available inside the event receiver code, so you'll be limited by CSOM's limitations.
      4. This is the only option to override events if you have O365/SharePoint online.
      5. Using this approach makes your code future safe, when SOM is killed finally.
      6. This is the list of events available to override.
   2. SharePoint Event Receivers (SER)
      1. No additional infra required to host event receiver code.
      2. Works using code running in context of W3WP.exe in case of farm solutions and spucworkerprocess.exe in case of SandBox solutions.
      3. Full fledged SOM API is available in case of farm solutions, no limits.
      4. This is only available in On-Premises environment.
      5. This might be deprecated or unsupported in future releases.
      6. This is the list of events available to override in SER.

2. You have a choice only in case of On-Premises otherwise you HAVE to use RERS. However, to be future safe, you should start using RERs if it fulfills all your requirements as the App Model is the future of SharePoint.

3. Both will fulfill your requirements reliably and efficiently, the decision depends upon your decision about future readiness and investment in hosting another application.

4. This can be achieved by List Validation formula without using event receivers at all, in fact event receivers would be an unnecessary overhead. That would be the recommended approach to do it. You can refer this article to learn about it.