The President of the United States acts as the Commander in Chief of the US Military. Of all privileges afforded to the executive branch this is ultimately the most impactful. When congress approves a greater military budget they are essentially allotting more power to the President. This may make sense based on your political views as well as the circumstances of the day, but ultimately the greater portion of military spending vs the spending on the rest of the government is what sets how much the country is a dictatorship.
Congress passes the budget and so acts as a tap on the flow of money, and as such power, between the different branches of government. An underfunded branch could disappear while an excessively funded branch could hold excessive control. If 100% of the funding goes to the executive branch, one person, you are at least a defacto dictatorship even if that branch has yet to do anything oppressive. Giving no funds to the executive branch, more likely manifesting in putting the military under another branch of government, you end up with a military that functions at a snails pace as every major decision must be debated and agreed upon. Again, depending on your political views this may not be a bad thing, but I wouldn't recommend it during times of active war.
In between there is a spectrum ultimately represented by the allocation of funds. In the end the military budget shows congress' trust in the current executive branch to handle it's power appropriately. I would argue no individual could be trusted with more power than a larger governing body, but that's up to the country to decide.