Common causes are things like software upgrades and database changes. There's probably always a way to avoid it but going down for maintenance might be less eff

Common causes are things like software upgrades and database changes. There's probably always a way to avoid it but going down for maintenance might be less effort and cheaper overall depending on the site. For example, if you can do it during a known time of low traffic or when you know users will just come back later. I've noticed several UK bank websites go down for maintenance during the night.