Well, if you made a mistake, like me, of ordering a MacBook Pro with too little SSD. In this case 256GB is really too little, then you are going to spend a lot of time getting rid of stuff. With most Macs, if you are writing code, using Dropbox or Google Drive and Homebrew, you are going to have a lot of caches.
On my personal machine, I typically only have 45GB free most of the time and that is even after turning off Shared Albums and deleting most stuff. So what is a person to do?
- Get Space Gremlin. Yes, it costs a little bit, but the graphical representation of your drive is really useful. The main confusing thing in Cataline right now is that it actually shows two different layouts so it looks like you are using twice the disk. This has to do with the new disk layout they are using. Just look at the stuff on the right. This representation called a "squarified treemap" is just awesome
- In terms of things to delete, I found a monster file in /private/folders which turns out to be cache files. There was a 20GB file from 4 years (?!) ago which turns out to various caches used by the system. You can safely delete them as they will be recreated. Fun fact, they are using hashed user id to make up these crazy names. And there is a tool I had not heard of called getconf which does an environment pull for things like DARWIN_USER_CACHE_DIR
- Move your big folders like Photo.library to an external drive. This is one trick you can play if you have a really large photo library. Just move it offboard. The trick is to use Option and then click on Photos and choose create New Photo Library and navigate to your external drive. Then you go to Preferences and choose Make System Library and this will live in the external.
- Move User Folders. If you are really running out of space, then you could just move your entire user folder set to an external drive. This means nothing will work without your external drive though, so beware. You do this in System Preferences > Users & Groups. Then right-click on the user icon and you will get Advanced Options and you can change the share location.