Disclaimers can be shown in court if it comes that far. If you seem to be an expert on something but make a mistake you can get into trouble for practicing [law/medicine/...] without a license. By putting in a disclaimer you make it clear that while you seem to know something you are not claiming to be an expert which can protect you. If you actually are an expert it is even more important because someone might take your generic advice as specific even though there is some complex detail about their situation that makes it not apply.
Most of the time this won't matter. People and courts generally know advice isn't to be trusted, if this goes to court it will probably be laughed out before they even see your disclaimer. However since there is trusted advice on the internet and courts/the law hasn't figured out where there is always risk and a disclaimer helps protect you against the court deciding you were playing an expert.
Of course I'm not a lawyer, I'm only guessing as to what will happen. I'm reasonably sure no lawyer will comment on this for reasons above.