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What is the purpose of paralleling capacitors on the input/output of a power converter?

In the design of a power converter, picking the appropriate capacitors for the input and output of the converter is quite important. It is relatively easy to calculate the necessary values for a given application.

However, in many datasheets it is suggested to use a capacitor network instead of a single capacitor. This is achieved by taking capacitors of a lower value and paralleling them until the desired value is achieved. Often, electrolytic and ceramic capacitors will be combined. I can think of a few reasons why:

 * Lower ESR (as the resistances are now paralleled).
 * Increased reliability: capacitors are a very likely source of failure for a power converter, if we have a few in parallel then we can survive one or two being blown out.

Are those valid reasons to have several capacitors on the input/output of a power converter? What other reasons are there?