A certain understanding of the circuit diagram is to better layout and optimize some deficiencies in the original layout. For example, whether some lines are reasonable, whether some signal lines need special treatment, and whether some lines that do not take large current can be reduced.
Understand the problems in product follow-up testing, with the aim of judging whether these problems can be completed by layout optimization. For example, whether some sensitive places need to add some shielding rings and so on.
In short, optimizing the circuit requires a comprehensive understanding of this product. Since it is optimization, at least improve the performance or reduce the layout area. I hope it helps you.