WordPress Object Cache and ENABLE_CACHE

An article by Jeff Starr suggests that to benefit from WordPress’ native caching capabilities, that define('ENABLE_CACHE', TRUE); should be included in the wp-config.php file. There also appear to be similar gists that allude to using define('WP_CACHE', true); and define('CACHE_EXPIRATION_TIME', 3600);

In an attempt to understand these better, there appears to be little to no information on the use of these declarations.

1. Are these necessary?
2. How do these improve the performance of a WordPress site?
3. Are there any downsides on using these?