Just an assumption Mr Simpson. but the inside corner of the post is actually all cut free and is being held like a post in that inside corner for the length of the grove the one bolt is going to hold the apron to the leg assmbly on the one side and the corner brace is holding the other side threw a possible glue joint. without the bolt the then all you have is the corner brcea and the inner piece of the legs isnt to sturdy, its been cut on all side and just a filler sorta speak for the length of the joint.
If in Doubt, Build it Stout!
One hand washes the other!
Don't put off today till tomorrow!