That really depends on what you want to learn and how deep. If you're automating things before the hypervisor comes online or there's an OS running (e.g: working on datacenter automation, bare metal as a service) you will have many gaps

If you want to run something like GNS3 network simulation on a hosting service's hardware you'll either have to deal with hiring a bare-metal server or deal with nested virtualisation on other people's VM setups. Network simulation absolutely drinks RAM, too, so just filling an old Xeon with RAM starts to look very attractive in comparison to cloud providers who treat it an expensive upsell.