Spam
Cost, Time, Content
Cost
The more time people spend reading and deleting spam emails, the less time they spend actually working and making money. Therefore, spam costs people money.
Time
Someone who gets a lot of spam emails waste more time on their email than people who don't. Spam takes up a lot of time.
Content
In some spam emails, there are links to other websites that can end up being frauds or viruses. So it is bad to ever click on a link in a spam email, or reply to the spammer.