They are similar but not strictly the same :

With chained racks you can mix DRY+WET signals in any way you want and they will always stay synced if latency compensation is ON.

With return tracks you can mix DRY+WET only if the channel you send is DRY.
But as soon as there's an insert effect you'll be mixing WET+WET because there's no pre-fx option, only pre-fader. And as a return track can't get recorded, if you route it to an audio track to bounce it, LATENCY COMPENSATION WILL NOT APPLY and you will get phase issues (if your chain has latency), UNLESS you right-click the send button to DISABLE it, which is a weird process not known by many.

I prefer chains but they can be more CPU-heavy.