You can usually tap once for extra rewards before merging. For some higher-stage items, a second or third tap might work, but more than that won’t give anything extra.

I’ve seen those tips about tapping stars and veins too, and it really varies depending on how you play. Sometimes doing it once helps, but other times a second tap gives you a bit more control, kind of like practicing daily word challenge to build intuition.
It ’s mostly about finding what feels smoother for your flow. Try both ways a few times and see which one helps you merge more confidently. Everyone ends up developing their own little routine over time!