custom_label_1

If `custom_label_0` holds your primary segmentation dimension, `custom_label_1` typically holds the secondary one — usually margin tier or brand tier when label 0 holds ROAS. The point of having multiple labels is that product set rules can combine them: "Champion ROAS AND high-margin" identifies items where the algorithm should bid aggressively. "Champion ROAS AND clearance" identifies items where you should pull back because every conversion costs more than it earns.

Two patterns to avoid. First, don't use `custom_label_1` for variations of what `custom_label_0` already encodes — that's wasted dimensionality. If both labels are flavours of "performance tier", you've effectively got one tier with more granular buckets, which you can achieve with a single label using more values. Second, don't change which dimension `custom_label_1` encodes mid-flight. Once your campaigns reference "items where custom_label_1 = high-margin", changing the slot to mean something else breaks every campaign rule referencing it.

The slot is most useful when it encodes data that updates at a different cadence than `custom_label_0`. ROAS rebuckets weekly; margin tiers rebucket monthly when COGS changes. Mixing fast-moving and slow-moving data across slots gives you finer operational control.