On PHB 50 the totem warrior barbarian's 6th level wolf ability is
You gain the hunting sensibilties of a wolf. You can track other creatures while traveling at a fast pace, and you can move stealthily while traveling at a normal pace (see chapter 8 for rules on travel pace).
So, on PHB 182 the Travel Pace chart says that you can normally only move stealthily at a slow pace, but there is no mention of a restriction on travel pace for tracking. So the stealth benefit for the wolf aspect is useful at least. Fast movement is a -5 to passive Wisdom (perception) scores only. The portion on Tracking on PHB 183 states:
A character can follow the tracks of another creature, making a Wisdom (Survival) check when the DM calls for it.
Again, no mention of travel pace being a factor. A check of the DMG section on tracking, DMG 244, lists several modifications for checks to track, none of which mention travel pace. Even the chase section (DMG 253-255) doesn't mention anything where this part of the wolf aspect would come into play.
So, is the tracking at fast speed portion of the wolf aspect just for fluff, or is there some game mechanic it adjusts?