Does it make sense to enlarge "shared_buffers" for writing Postgresql?

I'm using Postgresql-11, with a traditional HDD as the physical storing device. I need to optimize the performance for writing. I have changed the wal_buffers from -1 to 512MB, that means that wal_buffers no long use shared_buffers. Am I right? I want to know whether or not it can improve the writing performance to enlarge shared_buffers. In my mind, it is used only for querying? The current value of shared_buffers is 2GB, my RAM is 8GB. I want to change it to 4GB. thanks!