Or HaChaim on Deuteronomy 23:23/אור החיים על דברים כ״ג:כ״ג

1 וכי תחדל לנדר לא יהיה בך חטא. "If you refrain from making vows this will not be considered as a sin for you." This can also be understood in light of a statement in Gittin 7 that "if a person experiences that his income is barely sufficient he should give some away as charity. If he has ample income he must certainly be charitable." In addition to this the Talmud states in Ketuvoth 66 that "if one wants to "salt away" one's money he will find that it decreases." It is a psychological truth that inasmuch as man is very fond of his money he is loath to part with it. A person may wish to counteract his natural tendency to hang on to his money by making a vow to G'd so as to obligate himself against his avaricious nature to give some of his money away for a worthy cause. This is why the Torah has to warn us that the consequences of not living up to the promises one has made in the form of a vow may be devastating.

2Concerning paying a vow late the Torah says that the party guilty of this is guilty of a sin, i.e. he may experience being deprived of someone his is fond of. Concerning people who fail to give charity the Torah says וכי תחדל לנדר, that even if the failure to make vows may result in your not donating to charity and this in turn may result in your own money-supply diminishing in worth or amount, at least you will not suffer the additional disaster of losing someone dear to you, such as when והיה בך חטא applies to you..