system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do stores like Walmart or Meijer have 25 registers yet only keep 2 open?
gpt
It doesn't cost much to install registers. It does cost a lot to pay people to stand next to them. Most stores have software that predicts how many customers they'll have that day & thus the absolute minimum number of employees they need. Sometimes they'll underestimate (and often managers are encouraged to staff a little bit under the software estimate to save money). But, usually they'll have the minimum necessary to get people through. 

On Black Friday they might need to have every register staffed, and they actually will be. Every other day, it costs the store nothing to have extra registers sitting there, and they will have just enough open to get everyone through (in a time they've estimated will not make you quit shopping there) & still make a profit.