
VMware snapshots are widely used for different purpose, but the main reason why they exist in vSphere is to help backup programs: using VADP a backup can start a VM snapshot in order to have a frozen file, copy it (or copy only the changed block with CBT and virtual hardware 7 or greater) and then release the snapshot.
Other usage are to have a just in point rollback during patches or big changes, but a recommended practice is to release the snapshot as soon as possible.
Large snapshots or broken or invalid snapshots are common issues in VMware virtual environments. And monitor the snapshots size it’s a must!