[2018] Cache Tile Size. Logic of use. Help pls.

Please help me. I very tired to search information about that. Please explain to me logic of use "cache tile size". I did not find the answers in the documentation.
I read tips "use smaller to draw" or "use higher for complex editing, like filters", but I need to understand logic to myself and make decision.
Why am I asking this question?
I saw a perspective in these performance settings! And I do not give rest to the difference in 4k when choosing 1024k or 1028k. This would not have been done just because... I think...?
I have hardware:
Windows 10
CPU i5 6600
GPU GTX 1060
My tasks:
I need retouch huge size img (many layers with using tool "brush").
with love.
