Producing wealth/culture/science in a city

[stormwriter]

How often do you guys not build any buildings or units, and specify the city to just produce wealth/culture/science? I can't figure out if it's a good idea to do this or not. It's usually when i run out of things to build in a city.
If 50% of the production goes to one of those three, where does the rest go?

[Arkalius]

I do it occaisionally. Sometimes I'll switch a number of cities to research if it will let me get a certain tech one turn sooner. I also like wealth when I'm low on cash or if I need to build up a big bankroll quickly for something (impending tech that will give me better units and I want to upgrade them, etc). Not every building needs to be built in every city. For example if your city has lots of excess health, you don't need to biuld an aqueduct. If the city's science output is dismal, then you can probably skip the observatory for now etc etc.

As far as where the "rest" of the production goes... it goes nowhere. Basically what it means is you get one gold/research/culture for every 2 hammers of production.

[The diplomat]

I almost never do it because I feel like in most cases, there is always something to build like a unit or building. Even if you think you have a big enough army, you can always use a few more units. And there might a building that you might need in the future.

Basically, it is rare that my cities have no buildings and no units worth building.