Depends very much on usage and the e-liquid in question.
Running higher temps can caramelize liquids. This is noticeable in a Darkening of the mix. These can usually be topped up once or twice but start becoming bitter/nasty over time.(Time to clean/dry burn/replace)
Running to cool can be almost as bad as the liquid is not fully vaporized but more cooked.
Lighter, less sweet liquids can be refilled many times with little to no change in flavor/vapor.
The main concern is recognizing when the flavor has started to change and acting accordingly. Longevity of a coil/wick cannot be measured in Days. It is a measure of Volume Vaporized and is directly effected by Usage.