What exactly does the Tracking Limit do?

To directly answer your question KennyEastMids, the Tracking Limit purpose was to signal time length for SpectraLayers tracking. 15s meant that only 15 seconds could be chosen for processing.

Time length limitation was eliminated since SL 7.0.20 version.
Hence now --we users-- don’t see the former max time Tracking Limit , since there is no such limitation. Conversely the Manual reflects this.

Let’s have in mind that this new feature upgrade was either solicited or coincident with a user request discussed here.