What’s the alternative? Apples Photo’s app is perfectly incapable of syncing photos between 2 Macs and a phone as far as I can tell. It’s not cheap and I’m yet to see it work.
Works extremely well for me. Set it and forget it.
You’re gonna be fine :)
You can set this in the photos setting. You have the option to store all content locally while also backing up everything in th cloud. However, none of my devices have the space for 357GB of photos so I default everything to “optimize local storage”.
"Favourites" seems to -almost- have this priority in that they'll more often than not be on the device regardless of age and whether you've specifically downloaded them but it's not -quite- there.
[1] It has been flakey as a weasel's taint in the past.
Besides syncing 357GB requires some serious internet which is a privilege of a limited few.
It does take a while for things to arrive at all destinations due to my crappy internet connection but for me it works quite well.