[@FalloutJack] I'd consider those closer to experiments than retrieval operations. Sometimes an SCP is too large to take back to a facility, or is in some cases a location itself, so they take the experiments to the SCP instead.

In the cases where they are trying to capture a creature or safely retrieve an object, or recapture as the case may be, they usually use a taskforce rather than the D-CLASS personnel. Though I'm sure exceptions exist.