You know it's important to have cash on hand in case of an emergency, but when is it okay to dip into that aptly named emergency fund? Some scenarios are so obviously emergencies - you lose your job and rent is due - but others can be iffy.

A new poll from Bloomberg suggests that almost half of Americans would have a hard time affording a $100 emergency, like a speeding ticket, medical bill or other unexpected expense. Many Australians are in similar situations as well. Consider the idea that maybe this says less about people's financial habits than it does the garbage economy.

When you live paycheck-to-paycheck, you usually feel at the mercy of your employer. If you're lucky enough to have a fair, understanding employer, that might not be so bad. However, if your employer is a jerk or you just don't like your job, you probably feel powerless and stuck. Here's how an emergency fund can help with that.

Especially when you're just starting out, self-employment can be unsteady. You're not sure when the next client will come or how long the gig will last. For this reason, one financial planner suggests doubling down on your emergency fund.

While the general guidelines for emergency funds are up for debate, most people agree it's a good idea to at least have one. While you decide how much money to put in yours, make sure you incorporate all of your small, essential expenses -- not just the big stuff.

Years ago, I switched careers and moved to a new city. Financially, I felt safe, because I had a small emergency fund. If times got tough, that was my safety net. Times did get tough. In one instant, I lost everything. If you've depleted your emergency fund, here's how to go about rebuilding it.

Having an emergency fund is commonly accepted (and good!) advice. When to spend it is addressed less often. To make it simple to decide when to use it, define what it's for first.