Some believe that Biden's appointment bodes well for a deal to be struck between the UK and EU.
In addition, Biden's Irish ancestry has led some to believe that the US will side with the Republic of Ireland rather than the United Kingdom if disputes do arise post-Brexit.
The question surrounding what happens at the border between Ireland and Northern Ireland has long been a sticking point in Brexit negotiations. The withdrawal agreement signed by both the UK and EU included a piece of legislation which states that there would be no customs formalities at the border i.e. Ireland and Northern Ireland will be treated as a single market area for EU purposes. This is deemed a requirement to protect the Good Friday Agreement.
More recently there have been rumblings and murmurings that the UK government may renege on the withdrawal agreement. This was demonstrated in the UK government's Internal Market Bill, which included provisions to override some parts of the withdrawal agreement.
Donald Trump was an avid supporter of Brexit during his stint as U.S. President. If re-elected, this would have given some the perception that the UK would be looked upon favourably for a trade deal with the US once the UK leaves the EU.
However, it is quite clear that Joe Biden takes a different viewpoint. He and the Democrat party advised that they would not support a UK-US trade deal unless the withdrawal agreement was maintained and the Good Friday Agreement protected.