It’s important to read your thesis as part of your viva prep to refresh your memory: a valuable check against mistaken impressions and details gone astray.
It’s useful in another sense of the word too: the modern, computing sense where you refresh a webpage to see what has changed. You read your thesis but it’s you who is refreshed. You spot something, a new thought occurs or a previously unrealised connection is seen.
And a possible third sense: after so long spent bringing your thesis to life, it could be refreshing to read it and be happy that it is done!