Until recently, I (foolishly) believed that the capacitance of a given capacitor was the capacitance given by the datasheet +- the tolerance.
I recently learned about the DC derating of MLCC (multi-layer ceramic capacitors), which can be quite huge (I have seen some with 80% reduction in capacity). What's more, this derating curve seems to be missing from datasheets (you have to dig though the manufacturer's website to find it).
So, for filtering signals with a DC component (for example an RC filter), what kind of capacitors do you usually use? Do you still use MLCC and look up the derating every time? Or do you use another type that is more stable?
Sometimes, of course, you don't care at all about the precise cut-off frequency of your filter, and you can accept a factor 5 (or you can just derate by something smaller (50%?), so you know you will have an error one way or the other, but smaller.
But sometimes, you really have a trade-off between getting a well-filtered signal but still have the output of the filter changing "quickly" if the output changes, and then it would be nice if the cut-off frequency remains within 10-20% of what you decided.