Many people have debated the whether you even need edging. There are a few things you have to consider when you think about edging:
How big of beds am I planning?
How many beds do I have?
What am I covering my beds with?
I would recommend edging to people in the following cases:
Landscaping around the house
anything around your house should look neat and finished, other wise it makes your house look sloppy
You're using rock as your bed covering
if you catch a piece of bark in the lawnmower when you're mowing it's not a big deal, but shooting rocks out of the lawnmower is dangerous and hard on the mower
Here's a bed under construction that has edging
I would not recommend edging in the following cases:
You have very large beds
Edging may be simple looking, but can be expensive if you have to buy many rolls
You beds are located far from the house in the yard
Beds in the yard can be a little more rough around the edges, and without edging you can mow slightly into the bark when you trim around the bed. This will save you a little weed whacking.
You have many beds
If you have many beds, installing edging on each and every one would be time consuming and expensive