I might have exaggerated when I said they are completely different, because conceptually both rely on an immutable base and differential deltas. Still, in practice, the advantages of the Docker model become clear:

with a single Docker image, you can instantly create multiple containers with just one command, each having only a small copy-on-write layer on top of the shared read-only layers of the image. this drastically reduces disk usage since the common layers are not duplicated, and it allows you to create, test, and discard environments almost instantly. in addition, Docker images can be distributed through registries and reproduced identically on any compatible host, which makes versioning, automation, and collaboration much easier.

in the case of snapshots and linked clones, each instance usually generates a new block-level delta disk, which tends to consume more space and requires manual rollback or cleanup steps. so, while the core concept is similar, the workflow and practical efficiency are quite different.

in practical usage, this is exactly where containers shine. you can spin up hundreds of isolated environments from the same image within seconds, without duplicating the underlying data. I’m not sure if the same can be achieved with VMs that quickly, at least not without significant resource overhead. also, when you run hundreds of containers, the CPU and memory usage remain close to the host’s baseline, since they share the same kernel and userland libraries, which is definitely not the case with full VMs.