We almost always pay for hosting space. And, the fewer data, the faster access to it. This means that the loading of pages will be faster.
- Selection of identical blocks
Because site pages are quite similar to each other (they have common parts such as header, footer), then storing such blocks in a single copy saves space a lot. This allows efficient caching of page parameters (e.g. currency switching) or user sessions. Configurable here.
- Compression
Also, by default, the cache is stored compressed. It is used for:
- saving space;
- to speed up the delivery of pre-compressed content.
Configurable here.
Also, the small cache size allows for more efficient use of in-memory caching technologies such as Redis and Memcached. This is actual for highly loaded sites.