Go インポートで空の識別子を使用する場合とその理由は?

package main

import (
    _ "github.com/jackc/pgx/v4/reflect"
    "github.com/jackc/pgx/v4"
)

func main() {
    conn, err := pgx.Connect(ctx, "user=jack password=secret database=world")
    if err != nil {
        log.Fatal(err)
    }
    _ = conn
}

package main

import (
    _ "github.com/go-redis/redis/v9"
    "log"
)
func init() {
    // Set up global Redis client
    client := redis.NewClient(redis.Options{
        Addr: "localhost:6379",
    })
    if err := client.Ping().Err(); err != nil {
        log.Fatalf("unable to connect to Redis: %v", err)
    }
    clientInfo, err := client.Info("Memory").Result()
    if err != nil {
        log.Fatalf("unable to get Redis info: %v", err)
    }
    log.Printf("Redis info: %s", clientInfo)
}

func main() {
    // Do stuff with the initialized global Redis client
}