Photos sync'd from phone to laptop making pics taken instantly available to share via desktop apps. Also add in the NAS and you have three copies before you consider RAID or BTRFS or anything.
Replace Dropbox with syncthing and you have multiple folders and can choose which folders go to which devices.
Put a NAS at a second location and you have the ability to power up and power down the remote NAS whenever you want to make a backup and syncthing will handle the rest.
Add in any one of the UIs over the files on the NAS and you replace most of the household use of things like Google files or drive.
About the only thing I would like and don't have, is syncthing with an object storage backend for cloud based folders fully under your control.