Netflix lets you set up a maximum of five different logins on your account, and this typically lets you grant access to someone else in the family or means you can keep the kids' viewing history (and recommendations) separate from your own. However, even if you're the only person who uses your Netflix account, these extra user logins can still come in handy.
Think about the basic principle behind them: They keep viewing history and viewing recommendations separate. As a result, you can have one login to indulge your love of action movies and one login to concentrate on those cerebral foreign detective dramas you're so fond of. More simply, you could use one account for films and one for television shows. It makes life easier when you're trying to find something you're halfway through.
If you have a significant other, have one account each and then one for joint viewing, so those Mad Men marathons you take part in together don't necessarily have to interfere with your individual recommendations and history.
We're indebted to @shutupmikeginn for the idea, who suggests one account for your sober self and one for your drunk self. Another very useful approach you might consider if no one else to shares your logins.