Nigel's answer applies nearly all of the time. My comments are not really an exception but rather additional information that might be interesting to some.
A. Most everything changes with time. Electrolytic capacitors change over the years and so much so that slowly charging them up so they can re-form is required. This might apply to a capacitor or electronic device that's been sitting idle for 20 yrs or more.
B. A fully discharged capacitor presents a substantial load to a power source when power is first applied. Sometimes a circuit might contain a means of limiting that initial current surge in a way that lets the capacitor charge up just a little more slowly before going into operation as intended.
Again, more information than you probably need.