We are using Lambda to export CloudWatch metrics to another system. Haven't exceeded the free tier of Lambda yet, and CW itself was only $5 last month.
Having a t2 up the whole time would have been way more, plus it would have been subject to our Chaos Monkey.
Wouldn't it be a lot cheaper if you have a dedicated box where you can run your own VMs and add and remove services as you please? So far, running one at base cost with leased hardware costs about 1/10th of any 'cloud' provider out there, with lots more resources to go around. Right now, if want to spin up a new instance, container or process, I can do it locally, in vagrant or on a VM on the dedicated box all with the same config and management ease of the configuration management stack (we use SaltStack). It also works just fine with stuff like GCE or AWS, but those simply are never ever the 'cheapest' option. At best, they are a in-between solution when we need more hardware. It's great for temporary scaling, but of nominal resource usage there is no point in using those services at all, at least for us. The cost of a dedicated box is static, no matter how much you use, and yet it is always lower than the mean cost or 95th percentile of any AWS/GCE kind of thing. For (converted currency from euro) about 100USD we get 16 E5 cores, 92GB RAM, 1TB SSD RAID10, 10TB HDD RAID10 and 8TB transfer on a dual 1Gbit link. For the life of me I can't find any combination on Amazon to match that.
Having a t2 up the whole time would have been way more, plus it would have been subject to our Chaos Monkey.