References are an excellent way to confirm someone that someone did actually work at a particular place in a particular role and that they are not a total asshole. Beyond that, unless you know the reference well, I think they can be unreliably.

The reference knows the candidate and likely feels a much closer connection with them than they do with you. Assuming the candidate isn't an asshole, they will want to help them out by giving them a good recommendation. If the candidate was let go due to downsizing or such, the reference may even feel pressure to help the candidate find a new job.

So it's a great data point to have and as you say, it can help weed out the straight up liars.

But any 2 given candidates with 5 years at Acme Inc are not interchangeable. Some candidates are just better at programming (or some subset of it) than others, and I think employers try to find ways to predict that at interviews.

One technique I have found works is to do incorporate your own open source code into your work. Then when they want to see samples you have commercial quality code that isn't company property.