Steps to reproduce

When creating a new migration in Rails 6:

class CreateProducts < ActiveRecord::Migration[6.0]  
  def change    
    create_table :products do |t|      
      t.string :name
      t.timestamps    
    end 
  end
end

A new option, precision is created:

    t.datetime "created_at", precision: 6, null: false
    t.datetime "updated_at", precision: 6, null: false

The change was introduced in this PR:

#34970

Following this discussion:

#34956 (comment)

It seems that, initially, the goal was to solve a problem with MySQL version updates, but for some reason, the subsequent PR targetted all Databases, including Postgres.

My question is: Is there any good reason to explicitly specify the precision of the timestamps by default in Postgres? If so, would it be possible to document the reasons somewhere?

System configuration

Rails version: 6.0
Ruby version: 2.6.3