What volt range is needed by the device which you intend to power from the converter? That will give you an idea of acceptable error.
Suppose you are making an inverter. House voltage can wander by several volts. That is several percent.
Suppose you wish to power TTL IC's. They operate between 4.75 and 5.25 V. That is 5 percent above and below 5V.
It's a good idea to aim for tighter regulation than 5 percent, of course.
You must allow a boost converter sufficient time to reach desired output voltage at power-up. It can require many cycles.
And when you increase or decrease the load, it may again require many cycles to reach desired output voltage.