There are basically two types of junk mail: the junk mail one receives through snail mail and the more popular kind which is received through electronic mail. Both of which are similarly unwanted. Both type of junk mail are a nuisance and are thus annoying. They both occupy space (gigabytes and mailbox space) and they consume time to be able to get rid of.
The junk mail you receive through email can be such a headache. Imagine receiving hundreds of advertising emails through the email, and having to go through each of them trying to find which ones are relevant and which ones are not. It is also annoying having to find one important email in the middle of the junk emails.
Most major email providers have a junk mail filter. The likes of hotmail, yahoo mail and google mail provide an email filter which lets you mark a type of email as spam and you never have to deal with receiving these emails in your inbox.
Junk mail filters basically filters the junk email and immediately sends it to a bulk folder. The email user does not have to deal with seeing these junk emails in their email inbox. It is immediately filtered to the blouk folder which makes it easier to look for the important emails and easier to delete all the unnecessary emails. Junk mail filters essentially see similar emails and those which are similarly marked as spam are filtered to the bulk folder.