You can safely use loopback on ports where you either need it or where you want to record a special submix.
As soon as you enable loopback on a HW output / submix the following happens.
The loopback signal is there at the input and can be recorded.
If you have something connected to this particular input, then the audio signal is not lost, you can route it to another free output of your choice, enable loopback and record it on the corresponding input.
For the loopback signal at the input you have no metering, you need to watch the metering on the HW output where you activated the loopback.
Whether you can keep it enabled all the time depends on your needs. Either the port is free for this purpose all the time or you simply need to use this input for other things than loopback, to be able to record from this HW Input.
If you have a Babyface Pro and do not use ADAT7+8 IN/OUT, then I would use that last stereo channel pair for such purposes.
You can use the mirror function of TotalMix FX to mirror the HW Output of "Main Out" to that channel and enable loopback there.
Then this port ADAT 7+8 OUT has always the same submix as "Main Out" and you can use Digicheck with ADAT 7+8 IN.
BR Ramses - UFX III, 12Mic, XTC, ADI-2 Pro FS R BE, RayDAT, X10SRi-F, E5-1680v4, Win10Pro22H2, Cub13