Fuel tankering has always been cost consideration first. While the price per litre/gallon may be cheaper at your intermediate stop, there is usually a price per litre/gallon from the delivery system into the jet... Thus tankering may be the way to go.
Then there are operational considerations... such as turn times. Some airports charge by the hour for parking. In some instances if you go 1 minute into the next hour... your company gets charged for the full hour. Then there is a matter of downline delays to avoid curfews too.
Alot goes into deciding whether or not to tanker.