The linked clone works similar to the snapshot technique. Snapshots work in a way that saves disk use: When you create a snapshot and make changes after this (as you work with the system inside the VM), VMware stores only the changed parts of the disk (sectors).
Linked VM clones work similar: If you have a 10 GB disk and create a linked clone, you do not need additional 10 GB of space - just much less. As you work with the original or cloned VM, only the changes or differences are stores. It is important to note, that the cloned VM still depends on the original disk image.
But: You can work with both VMs independently - the differences is only internal. You save disk space when using a linked clone - but the performance might also be less in certain cases.
If you have lots of very similar VMs to run, it might make sense to use linked clones, as you can save a lot of disk space.
If you just clone a VM and then start installing totally different software or data, a copied clone might be better.