A: With many digital effects pedals, the incoming analog signal from the guitar or other instrument is converted to digital, processing is added, then both the dry and the wet digital signals are converted back to analog to be sent out to your amp or other effects boxes.
With the Flashback X4 (and other TC digital pedals, such as the original Flashback, which remains available for those who don’t need the extended features of the X4), the signal from the guitar passes through without being converted or altered in any way. A portion of that signal is split off and converted to digital, processed by the effect, then converted back to analog and blended back in with the unprocessed dry signal.
So, in a nutshell, the dry analog signal from your guitar is never converted to and from digital. Some players feel that this provides a more “pure,” uncolored result.