Ideally, you have a Single Configured Routing of Activities to import into the Line Balancing module along with a build list of units (or model/option take-rates) which determine Activity occurrence.
I say, ideally, because a configured routing contains all of the Activities that the assembly line could experience and the model/option properties reduce Activity duplication while also ensuring that those Activities shared across product variants occur in a minimal number of Operator/Station assignments (ideally only one).
For example, if I have 10 models and an common Activity is used for 6 of them, then in a configured routing line balance, I have only 1 Activity to assign vs 10 . The precedence rules apply to and from that one Activity instead of between 10 mutually exclusive parallel Activities.
Alternately, if I had imported 10 model-specific routings, I would need to define 10 unique precedence networks, and plan the location for 6 identical Activities. If each of those routings had 100 Activities, and if 60% were common, then I would have (1,000 Activities to assign in a model-specific routing situation, vs 60+(40*10) =460 worst case Activities. I say "worst case" because even those 40% Activities not common to all models are likely common to other models, so the real number is probably just over 200 Activities (vs 1,000). In short, creating a line balance from a configured routing is 5 to 10 times easier on average than importing and managing 10 unique model-specific routings.
When importing multiple model-specific routings, engineers will often define a Group to link those 6 different Activities together so that one one is assigned, the other 5 follow. This approach will work, but it is additional effort which will slow down the line balancing calculations and make the Precedence network and Yamazumi charts unnecessarily complex.