Zero reclaim feature allows  the system to automaticaly  reclaims continuous blocks with zeros (of 1GB granularity) and mark them as usable space to be leveraged by other zfs. Once reclaimed, the reclaimed space will be calculated and added to the available space of the pool, thus increasing the overall usable pool capacity. The mechanism of this feature works similar to only compressing zeros and is therefore listed as a compression option.
Yes, by enabling the compression options, the system performance is always impacted as the compression/decompression process would somehow occupy system resources at certain level.