Many times I use the SE to recover from REX economy crashes, especially if my REXing was via conquest. A great example:
Last monarch game I played as JCaesar I lucked out with bronze and seafood in Rome's BFC, so I built a bunch of axes and rushed both Pacal and Asoka (who had founded buddhism) while IW came in. I also had a settler being built and settled right next to iron as soon as the tech came in. Pottery->writing came next while I built Praets and killed Wang, taking three of his cities while having built two more of my own and taking an awesome barb city (for once one had popped up somewhere useful!!).
Now I have 10 cities by 0AD and NO way to support them with the science slider anywhere above 0%. Two things saved me:
most important was that I had built and stole enough workers to keep improvements/chops coming, and second was a
heavily micro-managed SE. I whipped some libraries in the high-food cities and ran scientists while working as many high-
tiles as I could. It took a TON of micro-managing to do this, but I had no option: do it or start disbanding units. The sci-guys kept research alive and the commerce tiles supported by overly-large army and huge maintenance bills.
For a time I was even running at negative income at 0% everything while living off of war spoils. I lucked out and bullied about 10 turns of alphabet from Pericles, bulbed currency with my first GS, and from there things turned right around. I had tons of GS points and popped several GScientists, settled a few in Rome with an academy. I was (amazingly) the first to metal casting and turned Delhi into a GMerchant headquarters with a forum and Colossus (never did get a GProphet for the shrine tho
). Currency trade-routes with so many cities was a godsend. With forges humming across the empire I whipped out a ginormous catapult-heavy army and smashed Pericles. Soon got maces (many CR2 or better, upgraded from veteren axes and praets)/trebs/knights rolling and squished Sitting Bull while vassalling Pericles ftw around 1150AD.
Of course, having three additional capital-grade cities in addition to Rome didn't hurt either
Maybe it was more of a hybrid WE/SE...