Cost, Time, Content
Time: Having to use up time to sort through spam or unwanted emails/texts.
Content: Tricks to get you to cause Malware to spread.
How should you avoid?
A second way to avoid spam is not replying. You shouldn't reply because your validating the email for whoever sent the spam to you.
A third way is to use one email adresses, some sites provide these so whenever you see it try and use it. This is so you don't get spam from them and get tricked.