is sidecar is where one can draw a picture on an iPad, the place that jpg into a MacBook "pages" poster with type?
or
one can move the iPad screen over to a MacBook to finish a project?
IMO, I have not found sidecar works well, if at all, for that.
Sidecar has two modes: extend the Mac display - in which case it becomes like a small second monitor, with very limited touch functionality, and if you try to use the Apple Pencil it often lags and the pencil tip is often not aligned with the cursor location. Basically it is only useful as a "dumb" small second display for the Mac.
The other mode is is mirror mode, which can be useful for some things. In this mode the Mac screen is duplicated on the iPad, which means you can simultaneously work on a document on the Mac and on the iPad. So for example, if you have Photoshop open, and for example using the Lasso tool, you can either draw the Lasso outline using the mouse/trackpad on the Mac, or you can draw the Lasso outline on the iPad using the Apple Pencil. For certain things, it is much easier to draw freehand with a Pencil than with a mouse/trackpad. (Thinking of your cartoons!) So this is useful going back and forth from mouse/trackpad/keyboard to Apple Pencil.
However there is one big caveat: in mirror mode the resolution and aspect ratio on the Mac is reduced to match that of the iPad (so it can mirror exactly). This is another reason to get the largest (12.9") iPad, if using sidecar.
But I still think it is more effective to use iPad with iPad apps, and Mac with Mac apps, and sync files via the cloud.
For example, I use Adobe Fresco to draw graphics on iPad with Apple Pencil (which works well), then open the file in Photoshop on the Mac, syncing via Adobe Creative Cloud.
Using Photoshop Mac app (or any other Mac app) on the iPad via sidecar is kind of clumsy, IMO.
Sure would like to hear from any others who have found that they can really effectively use sidecar for anything more than just as a small extra monitor