An important part of messaging is understanding character limits because this can affect the number of credits you use when sending a message.
There's a maximum amount of characters you can use before your message goes from one SMS using one credit, to one SMS becoming multi-part and requiring two, sometimes even 3 credits.
Now that might not seem like a big deal when you're sending 1:1 messages, but if you're sending campaigns to large groups of contacts, your budget can double or triple in a blink and it can result in a nasty shock when the invoice rolls in.
For more details:
https://support.messagemedia.com/hc/en-us/articles/4413576543247-Understanding-Character-Limits