Judging from [this question](https://gaming.stackexchange.com/questions/68334/is-there-drawbacks-to-rushing-an-era), advancing to a new era *may* have this effects: 

>  - increased bonuses more from city-states
>  - unlocks policies
>  - makes your opponents think your are ahead in tech (at least in multiplayer)
>  - cities make more damages (or is it just the animation that changes ?)

But is that all (or true, at least)? I've heard in some "Let's Play" I was watching that changing era decreses the costs of past era technologies. Is that actually true?

There is a comprehensive list of changes you get by advancing to a new era?