The few times I've run across information of this sort in the plant comments area, it's been very helpful. I haven't really been one to shear back a lot of my plants mid-season, but I've been experimenting a bit more this year.
Other info is nice to have too; like the fact that Limelight Salvia, grown in zone 5b/6, is now a huge bush but still hasn't produced a single bloom. I would never have chosen it had I known this. IMHO, knowing the area that the Poster gardens in would be crucial to making an informed decision based on their comments, and that information is sometimes missing.