Renting the building blocks
The 'as a Service' family is best read as a question of where responsibility transfers. With IaaS, the provider stops at the infrastructure: they keep the physical machines, hypervisors and network alive; you get programmable primitives — instances, disks, load balancers, private networks — and build upward from there. It is the cloud layer closest to owning servers without owning any.
The freedom is the work. An IaaS setup can replicate anything a data center could run, which is why enterprises migrating existing systems land here first. But every piece above the hypervisor — patching, scaling logic, failover, backups — remains an engineering task. The industry's whole trajectory since (managed databases, PaaS, serverless) is providers offering to take more of that stack off your hands, for less control and a higher unit price.
Shared responsibility, precisely drawn
Cloud providers publish 'shared responsibility' models for a reason: on IaaS, a compromised unpatched VM is contractually your incident, not theirs. Security OF the cloud is the provider's job; security IN it is yours.