`external` vs `public` best practices

Apart from the public modifier Ethereum introduces the external one. Both may be called outside of the contract and inside (the later one by this.f() pattern). Moreover, according to the docs: External functions are sometimes more efficient when they receive large arrays of data. but there is no further information what does actually sometimes mean and if this efficiency gain is held also for inte

[t2wave]

externalは引数をメモリ確保しないのでpublicよりガスが安くなる