Cache Files

Cache files are mainly used in Lookup transformations in Informatica
2 types
Static cache , Dynamic cache.
Both are used by connected lookup
Unconnected lookup uses only static cache.

If Lookup SQL Override is used it uses Index cache and Data Cache
Index cache -  Stores key columns ( i.e on which index present)
Data Cache - Stores output values.

These 2 files sufficient memory allocation is important aspect in case of lookup optimization. If the memory allocation is Auto, make sure that Maximum Memory Allowed For Auto Memory Attributes , Maximum Percentage of Total Memory Allowed For Auto Memory Attributes is defined properly.

Actually the answer is partially related to the Question.......

t/rs like Joiner, Lookup, Aggregator,Rank Transformations uses the Caches.....

aggregator
joiner
lookup
rank
sorter