It unites the country
You only have to look around to realise that Britain is no more unified than many republics – in fact, it's probably less so.
It's often said that the royal wedding and the jubilee brought the country together, but the vast majority don't participate in royal events, which have no lasting impact other than a bill for the taxpayer.
The reality is that monarchy has no real bearing on how united or divided a country is. In fact, the three European countries with the most active separatist movements are Spain, Belgium and the UK - all monarchies.