Getting in the habit of calculating runway and aircraft performance for every takeoff and landing is good policy no matter what you fly.
If I'm in an aircraft that uses set numbers (as opposed to a chart), such as tabulated data, I usually don't try to interpolate between the numbers. I take the next highest number and go with that. If, for example, numbers are published for slightly above and below my takeoff weight, I take the most adversarial numbers and go with those. That my performance might be a little better is just fine, but I'll take the longer runway numbers and the lower climb gradient information. If I can do better, great...but if I can't, then I've already taken that into account. Trying to split hairs down to the foot is assuming that you really can do exactly what the chart says.
In a Part 25 airplane, this should be the case, but in all cases, if you're calculating performance, adding a margin for safety on top of what the charts tell you is never a bad idea. If you're located where you're right on the margin of being unable to go, it's time to consider offloading cargo or fuel.
That soapbox aside, get in the habit of pulling out your data and doing it yourself, rather than just letting the machine find it for you.