I agree with userfriendly. I'm not an expert on this but from what I've read, cars that have been sitting around unused will be prone to sludge formation. Sludge is formed when water mixes with oil.

You may say that there is no way for water to enter the crankcase. The water in this case comes from the water vapor that is always present in the air. The engine has a breather that will allow air inside. If you've seen a dew covered car in the morning that's basically how water gets in. With the engine not running for long periods there is a greater chance for the water to accumulate.