Confused by when to use config vs opts

[tbelvin2000]

Hello,

I was setting up my neovim config and doing my best to follow the recommendation to always use opts instead of config when possible.
However, when loading Tree-sitter I ran into issues with it not highlighting python files without me explicitly enabling highlighting using TSBufEnable highlight.
After adding

config = function(_, opts)
    require('nvim-treesitter.configs').setup(opts)
end,

to the end of my treesitter.lua it seems to work fine.

I am confused as to why this was required, and if I need to do so for all of the plugins where I use opts={...} instead of config=... and .setup({}) as recommended in the documentation.

Thanks for any help clarifying this!