When making the transition from crib to a bed, some parents opt to go without safety bed rails, and simply put pillows on the floor. While this is certainly a less-expensive way to go, and does, indeed, protect the child from injury, it might not be the best solution.
Most toddlers are extremely active at night, in spite of being very sound sleepers. However, children need to develop a sense of the 'boundaries' of the bed...a sense that works even in their sleep. If you watch an older child sleeping, and observe what happens when they toss and turn and roll too close to the edge of the bed, you'll notice that they sense the edge and move themselves back away from it. This is the behavior you want your child to learn. They should be able to toss and turn, but only within a certain width...that of the bed. Pillows on the floor simply allow the child to roll right out of the boundaries of the mattress, and not be stopped.
Additionally, even though the child may not be injured, they can still be startled, and awaken crying. And, if you're like most parents, by the time your child is a toddler you've probably had enough nights of getting up in the middle of the night.
Safety bed rails, on the other hand, provide a visual sense of security for the child (and the parent). They can relax, knowing that they won't roll out of bed, and they will still develop the sense of the boundaries when they encounter the baby bed rails and have to roll back to the middle of the bed.
Modern safety bed rails are soft-sided, not the mean, cold-metal rails of days gone by. They help a child feel snug and safe, which, of course, they are.
One note about using safety bed rails: be sure to find a model that drops down out of the way easily. Leaning over the baby bed rails to change a diaper becomes quite a hassle after a while.
George - http://babybedrails.net - Baby Bed Rails