Very few creatures list their silhouette sizes. Some do in the "abilities" section of the creature description, but most do not, even ones that are unlikely to be Silhouette 1.
Since the Animal Bond is tied to Silhouette, this attribute changes from "nice to know (if you want to try moving it with the Force)" to "need to know".
Also, with the upcoming AOR book, Stay on Target , creatures will be used as mounts, and it is likely weapons will be involved at some point. If creatures are intended to be used in more-or-less the same way as vehicles, and follow the vehicle combat roles, it will be necessary to know their Silhouette.
Since much material has been published that includes some creatures, it may be better to have a note about how to determine Silhouettes for existing creatures. If the rules are "good enough" (is that a thing?) this may obviate the need for Silhouette in creature stat blocks.
Table 6-6 is simply too vague to be really useful. Some small things like speeder bikes are Silhouette 2 while large things like a fully grown Wookiee are Silhouette 1.
For example, the Stalking Acklay (p. 233) is 3 meters tall. I think that's not much bigger than a fully grown Wookiee. So is the Acklay Silhouette 1 or 2? Maybe it's much larger than its height suggests, since it's a six-legged beast. Maybe it's even Silhouette 3, the size of a small fighter spacecraft!
I have no idea, but as a player and GM I need to know.