For airplanes and shuttles, redundancy is beneficial while for languages, it is traditional and mindless. In other words, certain expressions are used without most people even considered the meaning of their individual parts. If they did, they would understand that the second term adds no value.
Two classic legal examples are null and void and terms and conditions. If an attorney wrote that the terms were null since they were unconstitutional, the meaning would be crystal clear with the exact same as when using the standard pairs. Similarly, when receiving an order to cease and desist, it makes no difference whether you cease or desist. Finally, there is the last will and testament, but either will arrange matters after your death.
Politicians are also guilty. The Congress has the Ways and Means Committee, the Budget Committee in other words, in which it tries to find the way (or is that the means) of paying for a budget item. Each and every citizen should be represented when either of them would include all Americans.
Even common folk are not completely innocent. Keeping something under lock is no different than keeping it under lock and key since without the key, well, there may be a problem. Your feel just as uncomfortable feeling pins as it would be pins and needles. Looking in every nook and cranny to find your glasses will lead to the exact same results as searching every nook or cranny. Finally, if everybody and his third cousin know about it, so does everybody.
Sometimes there is logic to doubling up. You need both nuts and bolts to attach something, even if the expression means the basic elements. Likewise, when older people talk about aches and pains, there is a difference between them, mainly in terms of the duration and strength of the unpleasant feeling.
So, as in poker, doubling up can be tempting but may not be the right decision. Think before you use a pair of synonymous words.
I would be interested in hearing if such useless pairs also exist in other languages. Let me know.