Addictine

I haven't ever used that feature, but on page 4 the manual states:

12. Cabinet Simulated Direct Out – Provides a transformer-tapped
direct output with cabinet simulation for studio recording or live
performance without mic’ing your amplifier. The ground lift switch can
be used to eliminate hum or buzz.

From: https://nl.line6.com/data/6/0a06434d8eea507efb30bdbdd/application/pdf/DT50 Quick Start Guide - English ( Rev D ).pdf

So I guess the advantage is not having to use a microphone and getting a simulation of the cabinet instead. Sounds similar to that Red Box idea on the Hughes & Kettner amps?