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You could take flats and darks on every night, and then use those flats/darks to calibrate the light frames from that night before all the light frames across all the nights for that object are registered and then stacked. DSS can do this (if you load each nights frames into a separate 'group') as i'm sure most other astro image programs can.
However, (unless the weather has been very dusty or similar) I would generally find it unnecessary to take flats on the same imaging setup on consecutive nights if everything has been left set up and is just as it was the previous night. I also only take flats against a twilight sky, and sometimes it isn't practical to take twilight flats every day (it might be cloudy, or i might not be home at sunset/twilight that evening etc). Especially with widefields with camera lenses, in practice I will often only take a new set of flats if I can see obvious dust marks etc in my images, in which case I will take them at the next available opportunity.
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