If you omit both CACHE and NOCACHE, then the database caches 20 sequence numbers by default. Oracle recommends using the CACHE setting to enhance performance if you are using sequences in an Oracle Real Application Clusters environment. Using the CACHE and NOORDER options together results in the best performance for a sequence. CACHE option is used without the ORDER option, each instance …
https://stackoverflow.com/questions/24298868/sequence-cache-and-performance