This is what we do with Netdata Cloud. We want to keep the FOSS agent as a powerful single node monitoring tool and use the cloud for free infrastructure monitoring. You can see ktsaou's comment above on how we intend to monetize.
It's because it was built with high granularity and unlimited metrics as a key differentiator from the beginning. The core is written in pure C, optimized to death. Even long-term retention was initially sacrificed, in order to be able achieve that high performance, with minimal resource needs.
Long term retention is now possible, but with relatively high memory requirements, depending on how many metrics are collected. Again, it was a decision to never give up realtime granularity and speed, even at the cost of writing our own timeseries db in C and utilizing more memory.
It's about troubleshooting. When you have a complex infrastructure, it's not enough to say that your db queries are slower than usual. Ok, so you immediately see that your db server is getting a lot more traffic. What was the root cause though and what can you do about it now? Given enough "funny charts", you can see for example that you have hit a resource limit that you can temporarily raise and also see that a particular component of your infrastructure has an anomalous behavior, e.g. a cron job that was usually utilizing resources for a few seconds, now takes minutes. So you can provide a quick workaround and move on to investigate what changed with that cron job.