Rapid Expansion

Assuming libraries have already been built in commerce cities and markets and/or grocers have not, you are presented with pursuing either banks or universities. As they currently stand either building provides an equivalent benefit (if rep specialists aren't taken into account). This is because both cost 200 hammers and combined with the dirt cheap and formerly established libraries net a total multiplier of 50% for either gold or research. Thus you will gain similar yields building wealth after pumping in unis(to push the slider high), or building research after pumping in banks (allow the slider to drop lower). Admittedly Unis are usually prefered because they unlock the coveted oxford right away rather then the banks which require more techs to unlock wall street.

However bringing markets or grocers into the picture, if they were built to provide bonus happiness or health, encourages the use of banks and build research since commerce will be multiplied more when it's turned into gold. This means building wealth to push the slider higher is actually less efficient than building research and keeping the slider lower.

Another way to think about it, is in comparison to binary research. One of the reasons binary research is used is to maximize the benefits of multiplier buildings. For example if I'm about to build a lot of beaker multiplying buildings empire wide, it's beneficial to save commerce as gold by turning off research temporarily. Then I can spend that gold after the science multipliers are built generating a greater number of beakers in the same number of turns, because each gold coin is now worth more beakers than when they were originally collected. This also works in reverse, empty your reserve gold before you put in a lot of gold multipliers, and it will be easier to recoup that gold after the multipliers are built. Build wealth and build research work along much of the same principals, in that its more efficient to build the one that has a lower aggregate empire wide multiplier. Of course binary research also has the handy side effect of allowing for easier monopoly tech research which is probably even more important since tech trades can double, triple, and even quadruple your beakers if you're savy and maybe a little lucky.

On a final note I'ld like to point out the usefulness of early gold multiplier buildings in a game that is using a lot of espionage. They come far before any espionage multiplier buildings and allow you to pump the EP slider higher and earlier. I haven't actually done the calculations but I'm fairly confident that 200 hammers for 25% gold boost+up to 4 happy faces>200 gold coins=200 EPs. In the recent NC game I did this to catch up in tech after three early wars and it netted me the lib race when I'ld only teched through Currency and Construction by myself while the most advanced AI was through philo, feudalism, theo, engineering, and civil service.