That's the interesting question -- what does my empire need right now? Does it need to grow some cities up to size 12 quickly? Does it need to build roads and irrigate tiles so that those cities will be productive?
Joining them, a few at a time as @timerover51 suggests, will help cities grow to work more tiles without increasing their flip risk.
Using them, in gangs of 3 or 4, makes sure that the tiles being worked are productive.
My bias / preference is to grow my cities more slowly, while keeping my lux slider at 10% in Republic and improve more tiles. I worry (perhaps too much) about unhappy citizens when I only have access to 1 or 2 luxuries. Perhaps growing my cities faster would improve my game play.
Joining them, a few at a time as @timerover51 suggests, will help cities grow to work more tiles without increasing their flip risk.
Using them, in gangs of 3 or 4, makes sure that the tiles being worked are productive.
My bias / preference is to grow my cities more slowly, while keeping my lux slider at 10% in Republic and improve more tiles. I worry (perhaps too much) about unhappy citizens when I only have access to 1 or 2 luxuries. Perhaps growing my cities faster would improve my game play.