Not everyone can fight with Q7s all the time. It's good to know what weapon your opponent is using and what their strength is so you can bare hand fight easy opponents and save your weapons for stronger opponents.
Before I had enough money to fight with Q7s regularly, I fight barehanded in 90% of my fights. I only used 2-3 Q7s daily.
Also when you want to maximize kills but still want to get the maximum rank out of it - you kill enemies requiring 2 or more hits with a zooka and use a Q7 on the 1-kill-enemies.