Should someone living pay check to pay check be going on a cruise

I don't get a lot of money in child support from my baby daddy because him and his wife live pay check to pack check and I'm about to get LESS because one of my kids turns 18 in August. He is involved with our sons though. He decided to book a cruise with his tax money last year to take our almost 16 year old on a cruise for his 16th birthday. He was able to hold the spot and pay it off slowly. So any extra money he put towards paying off the cruise. My son is going on this cruise with his dad in June. I have been thinking, of you live pay check to pay check should you be going on vacation? All that money he was putting towards paying off this cruise could have been building up a savings account. I just don't get why people who don't have shit on a savings account will put money towards a vacation.