The compression algorithm zstd brings faster compression and decompression, while maintaining a compression ratio comparable with xz. This will speed up package installation with pacman, without further drawbacks.
The imminent release of pacman 5.2 brings build tools with support for compressing packages with zstd. To install these packages you need libarchive with support for zstd, which entered the repositories in September 2018. In order for zstd compressed packages to be distributed, we require all users to have updated to at least libarchive 3.3.3-1. You have had a year, so we expect you already did update. Hurry up if you have not.
If you use custom scripts make sure these do not rely on hardcoded file extensions. The zstd package file extension will be .pkg.tar.zst.