Mostly is very usefull to know if one or another website is down. Here is simple example to monitor your websites:
sites.txt example
website1.com website2.com
Now you can add it to crontab. Type crontab -e and insert:
# ping websites every minute * * * * * /path/to/monitor-websites.sh > /dev/null
The script use my notification function to slack. This tutorial you can find at [Tutorial] send message with linux to slack
Example of message in slack if website is offline:
