Far too many times, one or both of my drivers did not pit on their scheduled lap. They end running another lap at a lower push level and either barely make it to pit in, or have to coast the rest of the way. For some tracks the fuel calculator is off, with Spain in particular being way off if you get DRS almost every lap. It would be nice if pit in laps and fuel were two separate options. It can be quite easy to forgot to check to make sure your driver(s) are pitting when they should when in the heat of battle.
If my strategy tells my drivers to pit on laps 11 and 12, I want them to pit on laps 11 and 12. I don't want them to go another lap just because they have enough fuel for 0.8 or 0.9 laps.