In daily life, it is best to get things in writing when possible, even if you do not anticipate being in litigation. It is possible that you might end up in litigation, or otherwise find yourself in a dispute. Written evidence is as powerful in an informal dispute out of court as it is in formal court proceedings. Court procedure mirrors informal dispute resolution procedure. Both parties are heard and put on evidence. Then, a decision is made. This is the same for formal and informal proceedings.
Tangible evidence is important, because it is common for people to think that they can say something in court that they heard someone else say, but this is usually not true. Such is hearsay. There are exceptions, but those are relatively rare. Basically, if someone else said it, you cannot testify to their statement in court.
People change their minds. If you remember someone saying something, they may not also remember it. Accordingly, they may not testify for you. They may not want to get involved as a witness in a legal dispute. They may forget what they said. They may remember it differently than you do. This is very common. As a result, valuable evidence that could be in writing is lost. Accordingly, your case suffers.
So, get tangible evidence whenever you can. If you are given a special deal, or exception from standard procedure, whether it is from the cable company, bank, auto shop, etc., it is prudent to ask for it in writing. The individual to whom you are speaking will not want to do this. It may allay some of that person's fears to say that you are not trying to get them in trouble and that your request is not directed toward them at all. You simply want to have something in writing in the event that you talk to another person from the same company who does not know of your agreement. If you follow this principle regarding tangible evidence, it could reduce frustration when you find yourself in a dispute.