TL/DR
Inserters should wait with items in hand, instead of with empty hands.Description of Change
I propose to make the inserter always grab items immediately, even if the assembly machine has the required amount of items, but then wait with inserting them into the assembly machine until it has used up enough items.Reason for Change
This is an attempt to solve the problem where inserters insert new materials into an assembly machine too late, because they wait until the assembly machine has used up enough items, and then it takes some time to grab new ones.Other proposals have been made to increase the number of items the inserter wants to have in an assembly machine, but this has been rejected for various reasons.
Pros: Items are inserted as quickly as possible with just a small additional buffer
Cons: The item buffer is increased by the amount grabbed by the inserter
All in all however, I believe this would be the optimal trade-off.