What is browser.cache.disk.amount_written in Firefox about:config and when edit?

Recently I decreased the capacity of cache Firefox uses by editing the following two settings:

1. browser.cache.disk.smart_size.enabled (new value: false,previous/default value: true)
2. browser.cache.disk.capacity (new value: 16384, previous/default value: 1048576)

What is browser.cache.disk.amount_written? It's value, at this moment, is 2039744. Should I edit this setting? When edit or delete?

Thanks a lot!