How and when to use duplicity verify?

I'm making daily incremental backups and monthly full backups, both with duplicity Daily backup script (in /etc/cron.daily/)

#!/bin/sh

adddate() {
    while IFS= read -r line; do
        printf '%s %s\n' "$(date):" "$line";
    done
}

# be sure external drives are mounted
mount -a

# backup to HDD backup B, using duplicity 
echo "\n\nBacking up /home and /etc into /mnt/backupB with duplicity (incremental backup)" | adddate >> /var/log/daily-backup.log 2>&1
export PASSPHRASE=****
duplicity --exclude='**/.cache/' --include /home --include /etc --exclude '**' / file:///mnt/backupB | adddate >> /var/log/daily-backup.log 2>&1
unset PASSPHRASE

Monthly backup script (in /etc/cron.monthly/)

#!/bin/sh

adddate() {
    while IFS= read -r line; do
        printf '%s %s\n' "$(date):" "$line";
    done
}

# be sure external drives are mounted
mount -a

# backup to HDD backup B, using duplicity
echo "\n\nBacking up /home and /etc into /mnt/backupB with duplicity (full backup)" | adddate >> /var/log/monthly-backup.log 2>&1
export PASSPHRASE=*****
duplicity full --exclude='**/.cache/' --include /home --include /etc --exclude '**' / file:///mnt/backupB | adddate >> /var/log/monthly-backup.log 2>&1
unset PASSPHRASE

My question is: when and where shall I use duplicity verify? After incremental or full or both?