You're not wrong in that it can be used but the very thin consistency makes it a bit too tricky to keep in the gluing surface without it wicking into the wood or running out of the joint.
I know one of the guys on Paleoplanet uses it thickened with the West fillers but that takes a bit of practice. Easier to just buy some of the thicker stuff.
Even West recommends using more appropriate stuff for the job.