I like to have a working mail setup on all machines as this allows to be notified about cronjobs that failed and also to be able to send other notifications that would otherwise be lost. It is also especially useful for things like git send-email or automatically sending GPG signatures with caff to others.
However, mails cannot just be sent from any device and mail servers on the internet usually reject mails from dial-up IPs or public WiFi networks. To fight spam, techniques like SPF have been developed that restrict the mail servers that are allowed to send mails for the domain name used in the
From: field. Therefore the best way is to relay all outgoing mail through the mail server that is responsible for your domains.
While most tools also allow you to configure an external SMTP server, it is on one hand tedious to configure it everywhere and on the other hand also insecure if you have to write the username and password for authentication to many user-readable configuration files on your system. Therefore I am running a local MTA on all the computers I administrate to relay mails to a central mail server.