...

1. Exactly Once Delivery. In KIP-98, the community introduces Exactly Once Delivery, which guarantees that every message will be persisted exactly once without data loss or duplication. However, in order to give the community time for upgrading, by default, the producer will still use at-least-once delivery and set "enable.idempotence=false".
2. N-1 failure toleration. If the brokers are flushing records to disks asynchronously, the strongest concurrent failure Kafka can tolerate is N-1. (i.e. N-1 brokers shut down before the memory messages flush to disk). However, for some performance reasons, by default, the producer config will set "ack=1", where the data loss can happen if the partition leader shutdown.

Having these guarantee won't have a significant performance impact, as stated here: 

An analysis of the impact of max.in.flight.requests.per.connection and acks on Producer performance

Public Interfaces

1. Producer config defaults will change in release version 3.0

...