We are starting to publish services from Pro rather than ArcMap. It appears that, you can share a web layer (only for federeated servers) from the share ribbon item or publish a service by clicking on the server in catalog. Are there any differences in the resulting service, especially in terms of performance?
As you mentioned you can share a service in ArcGIS Pro from the 'Contents' menu or the 'Share' ribbon. Which interface you choose to publish from will not affect service performance. When you publish a service through 'Publish Web Layer' from the 'Share' ribbon ArcGIS Pro will publish all the layers in your current map.
When you right click on a layer in the 'Contents' menu and choose 'Share as Web Layer' you are only sharing that individual layer. This makes it easier to decide which layers you want to participate in your service. You can also view which layers will be publish with your service from the 'Content' tab in the 'Share Map As A Web Layer' window.
Hope this helps!