I've been following the fall and fall of sterling since around June 23rd. I've tried to avoid commenting on it though because truth be told I still have no idea what the fall in exchange rate even means. It could still just be a short-term, panicky reaction that will recede if it becomes clear that Brexit isn't so bad as all that; it could be something that was going to happen anyway (as I think NJ has pointed out, the pound was already on a downward trajectory in the year or so leading up to the referendum); or we may not have seen the last of this and the pound is set to be 20% -30% lower for many years to come.
And while I don't know that I can't say I even know if the fall is a good thing or not. It's a bad thing for Brits who live or work abroad; it's not going to be good for prices of anything imported (although that might be minor if the fall doesn't last). It might be good for exports, but other effects may negate that or may not.
What *is* true is that this can't be brushed away as just your average foreign exchange market rise and fall. Sure, currencies go up and down all the time, but the last time this happened at this level was in 2008 as part of the global crash; the time before that was Black Wednesday, or the mid 1980s rush to the dollar that battered the pound and sets the "31-year-low" threshold we're seeing set afresh so often these days. And it can't be ignored that the pound falls whenever there's a story about hard Brexit, or fresh expectations that the UK will leave the Single Market, and rises on opposite expectations. You can't really point to the FTSE Stock Market boom either, since this is very strongly correlated with the corresponding falls in the pound's value. Finally, I don't see how the volatility in the value of sterling is helpful either. If it's worth $1.22 at the moment and basically stays there for six months then I suppose that's fairly manageable, but if it's $1.22 today and $1.20 tomorrow and $1.25 on Wednesday and $1.18 on Friday, and back up the week after that, doesn't that present its own risks, because while traders are happy to buy and sell pounds your average man on the street won't be? Yet that's often what the pound is doing, and I'd suggest it's the volatility that's the main problem right now.
I don't think we should pander to market expectations in deciding policy, but it might be worth at least considering them. At any rate, the longer the depreciation in sterling lasts the more it becomes something serious rather than just a temporary blip that can be overlooked.