You can even handle impressions/clicks/conversions in a lossy system, you just have to bound how much loss you're willing to accept. The counterbalancing factor

You can even handle impressions/clicks/conversions in a lossy system, you just have to bound how much loss you're willing to accept. The counterbalancing factor is how expensive you want your logging infrastructure to be -- the more consistency, the more it costs. The other trade off is availability: what do you do when the logging backend is temporarily down? Return a 503 to the user? Or accept that you're not making money on that impression and move on?