It would be really nice to be able to perform some sort of incremental file backup. We use file backups only once a week bacause it produces much load on our server. Being able to perform small incremental backups in between would be a nice benefit. We then would go to entire backup once a month and incremental file backup together with full db backup every day.
This idea was tagged backup, file, incremental on October 4, 2018 by 
Ulrich Esser.
Hi Ulrich,
This is actually our main feature priority currently. On the changelog – https://updraftplus.com/changelog/ – you’ll see that some of the internal pieces have been added over the last few pieces. We are getting very close now.
David
This is now released (in UpdraftPlus Premium 2.16.0).