Often, there are giveaways done by bloggers where you sign up and then get a course, ebook, information, or other useful information.
They can be hit or miss. If you don’t mind sharing your email then you can get some nice things for free.
I usually sign up for them then just get the items I truly think I’ll use. I used to get everything but I don’t know why (info hoarder anyone?) because there were some I knew I would just never use.
I do plan to participate in them someday. They can be a great way to grow your list. And even if you gain some and then lose some, you may add a few great and interested subscribers that love what you do.