This is a common reason that Sailors are known for partying after long deployments.

Imagine you are 21 and unable to spend money, have free housing (the ship) and free food, then you land in a foreign country where you can finally drink after 8 months at sea with all the money you saved.

It's high high's and low low's

This is US Navy-specific, and the person you are replying to seems to have a dated experience of when beer days are authorized. It's every 45 days underway without a port call in sight, and this is governed by formal published regulations. Most ships pull into port at least every 30-40 days outside of major combat.

Ground troops in Iraq and Afghanistan in the Global War on Terror were under General Order #1, which prohibited alcohol in theater, but elsewhere like Djibouti and Qatar were authorized three beers a day maximum.

How far we've regressed. 400 years ago you would get a gallon of beer per day if you were a sailor.