I'm surprised too.... all week it was red 'til last night when they said they had a draft deal on the border. So with today's news, I expected a massive green candle. I give up trying to predict the market.
It's easy to imagine that "markets" have minds of their own. Pithy market sayings like, "Buy the rumour, sell the fact," abound.
I, too, benefit when the GBP (£) is weak. It has been a good bet long term. Ten years ago the GBP was US$2.06; now it's just under $1.34. This year the bet hasn't been as favourable. We nearly touched a low of $1.20 in January before the GBP began to rebound from its post-Brexit tumble. My US savings (and pension when it starts in 2019) are denominated in USD, so things cost more now than they did in January. I imagine many people on this site are in the same position. (Thank goodness I bought Heidi's engagement ring in February when Sterling was only £1.22!)
It appears to me the GBP is in a very long term bear market in which this year's strength is a "bear market rally." We may have another month or two of the Pound rising against the dollar before it drops again for years. That's just my guess. The Exchequer and BoE have been driving the Pound down intentionally for years.
Beyond living expenses, currency fluctuations also affect people who are applying for visas on the basis of savings who hold those savings in USD or other currencies. In my case, I set aside USD savings in January equal to £62,500 plus extra to allow for some appreciation of the Pound. That US-based account was enough for the fiancé visa applied for in July. It's not enough for the spouse visa we go for next week.
Here's something we just learned about visas and exchange rates.
The fiancé visa is applied for outside the country, of course, so they FIX the Pound value of foreign savings as of the date you apply. It doesn't matter if your currency plummets against the Pound after that.
We're applying for the spouse visa from inside the UK, so the rule is different. The exchange rate is NOT FIXED. In our case, we'll be making in-person application at the Sheffield office. UKVI will determine the Pound value of my previously-documented US savings ON THE DAY we appear, but the account will almost certainly be worth less than the £62,500 requirement (unless the Pound drops considerably in the next week). We have had to document other savings because of it which, fortunately, we're able to do. Remember, you can't just add more money to your savings account; all your savings have to be traceable - seasoned in your accounts - for the last six months or longer.
If your savings are borderline, I suggest you don't take the risk of falling short come the day of your application. One easy option you have to eliminate exchange rate risk is to bring your savings to the UK when the exchange rate yields at least £62,500 after the conversion.