I've used a retractable lead for years with my small dog without any trouble at all and I've never had one break.
One of the reasons I use one is because where I often walk her there are a lot of high steep banks beside deep water and whilst her recall is very reliable, if she were to slip down one of the banks I'd never be able to reach her and I'm not sure if she's be able to get back out. It allows her to roam but keeps her safe and I don't have to juggle a long line. In the park she's off lead.
But, I wouldn't use one on a dog that was unpredictable or likely to bolt, nor would I use one on a large dog.
Retractable is no good when trying to train recall as pps have said a long line should be used for that.
I can't see the necessity or desirability of having a very long retractable lead especially for a small dog.
Also if you do use one the tape ones are much better than the thin wire ones which can snap very easily.
As adaline says they must never be attached to a collar.
They seem to be universally hated on here but used sensibly and properly with a dog that has been trained not to pull they're absolutely fine.
It's also wise to have a normal lead available as a retractable isn't suitable.