Most oscilloscopes have multiple channels which enables makers to debug their hardware designs. Many times these designs involve making time-dependent measurements across power domains. When these measurements must be made, a true-differential probe is required. This type of probe isolates protective earth (ground) from the measurement node by 2500V or even 5000V and possibly more.
This probe isolator design allows a hardware designer to make measurement across power domains within a limited bandwidth. By designing around low-bandwidth parts we can provide an isolated probe at a tremendous value.