Usefulness of constant current limiting in bench power supply
Limiting the current and the voltage effectively limits power, since power \$P\$ is the product of voltage \$E\$ and current \$I\$:

\$ P = IE \$

Since bench supplies are commonly used for prototyping, where faults are commonly introduced mistakenly, this is a big win. Many faults that would normally destroy a device will instead not destroy the device if the total power is low. This is because many faults destroy components by excessive power generating heat faster than it can be carried away, causing (often microscopic) materials to melt or vaporize. If the power supply can't supply enough power to vaporize your components, then this just can't happen.

Also in some cases it can be handy to have a current source instead of a voltage source. Driving an LED, for example. A power supply with adjustable voltage and current limits can be either a current-limited voltage source, or a voltage-limited current source.