What's new in macOS 10.13.5: Messages in iCloud
A few days after the iOS 11.4 update, macOS 10.13.5 has finally been unleashed for the Mac. While primarily focused on bug fixes, there are at least a couple things of note here in Apple's latest update.
We installed the latest build and scoured through for any noticeable changes. As often is the case, Apple outlined the biggest change right in the release notes.
Messages in iCloud, which arrives to iPhone's and iPads with iOS 11.4 is now available with this update. It can be quickly enabled by going to the Messages app, Preferences > Accounts > then tick the box that reads Enable Messages in iCloud.
Otherwise, no major changes were found, other than a very slight frame rate increase in games with using an eGPU.

macOS 10.13.5 was in public testing just over 8 weeks and saw 5 beta releases. Earlier this week, Apple also debuted the first beta of 10.13.6.
The release of macOS 10.13.5 follows the releases earlier this week of iOS 11.4, tvOS 11.4, watchOS 4.3.1, and HomePod firmware 11.4. It also precedes WWDC, where Apple is expected to release the first beta of macOS 10.14, as well as betas of their other software platforms.
We installed the latest build and scoured through for any noticeable changes. As often is the case, Apple outlined the biggest change right in the release notes.
Messages in iCloud, which arrives to iPhone's and iPads with iOS 11.4 is now available with this update. It can be quickly enabled by going to the Messages app, Preferences > Accounts > then tick the box that reads Enable Messages in iCloud.
Otherwise, no major changes were found, other than a very slight frame rate increase in games with using an eGPU.

macOS 10.13.5 was in public testing just over 8 weeks and saw 5 beta releases. Earlier this week, Apple also debuted the first beta of 10.13.6.
The release of macOS 10.13.5 follows the releases earlier this week of iOS 11.4, tvOS 11.4, watchOS 4.3.1, and HomePod firmware 11.4. It also precedes WWDC, where Apple is expected to release the first beta of macOS 10.14, as well as betas of their other software platforms.
Comments
So I don't get where messages in iCloud improves upon this. And, as another poster mentioned, more space in iCloud storage would get used with messages in iCloud...
Perhaps one of the main benefits of messages in iCloud is when you delete a message or an entire conversation that it gets deleted everywhere? I tried deleting both a message and a conversation in one device, and they remained in the other devices. Synched deletions seems like a good idea, but as I said, I rarely delete messages. Also, I can see a possible back-up benefit, but with so many of my Apple devices carrying the same messages, they are already being backed up through redundancy.
I year ago I dealt with Apple engineers for about 4(?) months because my iPhone and Mac wouldn't sync up messages. Anything sent to my iCloud email would go to my Mac (and only my Mac), and anything sent to my iPhone would go to my iPhone (and only my iPhone). Months of weekly calls with an open ticket and them trying different things, which included me installing Profiles to upload all my data dumps they eventually they just had to give me a new iPhone to get them to sync up. Maybe this will resolve that issue (maybe it won't), but if it happened to me, I knew it should be synced between all devices, and I was willing to spend months helping Apple resolve it, I have to wonder how many users have this issue and don't realize it's a feature or aren't going to bother getting resolved (perhaps because they don't know how to get it resolved).
We also can't rule out Apple have other plans for Messages in iCloud. I really doubt it was done just so they can optionally nickel-and-dime users for an extra 99¢ per month for more storage. I'm seeing an additional 11 GiB of data use by Messages, but since the 5 GiB tier is unreasonably small I'm already on the 50 GiB plan, which is more than enough.