as in adjusting it had minimal if any noticable effect on shifting assuming all other factors (cable tension, chain length primarily) were correctly set. The maximum adjustment possible with the screw was so small that in his experience adjustments did not generally make a difference. I'll take the word of folks here (well biked, operator, etc) that smallest possible gap between pulley and cogs makes shifting better but I am not sensitive enough a rider to notice the difference a couple of mills would make.
Try this.
Set B-tension to optimal, then max out b-tension like you don't know what you're doing. The shifting will be noticeably crappier. How much depends on the range of b adjustment and the specific derailleur. To get 100% shifting performance, b-tension cannot be ignored.