I wouldn't say it's not advised...just that it isn't 100% guaranteed. I successfully walked a 2BR at VGF just last month at the 7 month mark using some transferred in SSR points. I needed Th/F/Sa/Su, and I knew the Th/F days were going to be difficult, so I booked T/W/Th/F first. This prevented non-VGF owners from grabbing the Th/F nights. Sure, a VGF owner could have snagged Sa/Su and blocked me -- but my thought was that if a VGF owner didn't already book those days, they probably weren't going to book them just days before their home resort advantage expired. Therefore, the bigger risk to me was the large amount of people that were waiting to switch over at 7 months.
I think where people say walking at 7 months is pointless is for walkers that are trying to start their walk a few weeks in advance. In my case, I started only a few days, so it had a much higher chance of working.
Its also higher risk when you are walking into a really high occupancy time. Trying to walk into a BWV Studio at F&W at seven months is just not likely - because an owner probably will grab those days available - there are owners still making plans "last minute" and very few rooms left. That can be the problem with a lot of low supply options - you can see that their is a room available - but it might just be one. And it only takes one owner to extend his vacation into your day to have it disappear before you get there. One night gone in the middle of your walk and you are back to square one.