Until the 11+ has been and gone, the comments will have no impact at all. That applies even if the child has been opted out of the 11+ and has applied for Upper Schools only.
The notes for this "blank space" on the Bucks form say:
You can add reasons for your preference if you wish (it is not compulsory to fill in reasons), for example, any medical, educational or social reasons for your preference for a particular school. In these cases we need documentary evidence for us to be able to consider this Please note that not all schools consider applications under such circumstances, check the parents’ guide or school’s website for further details.
Therefore, the first time it will be looked at is on 11+ results day. What it is there for is:
a) information about attachments, special needs, church commitment, or special schools - anything exceptional that should be considered under the exceptions to the normal rules. It may just be used for mentioning further attached documents.
b) any other information, such as the need to be close to home. However, that can be a double-edged sword - what if the local Upper is closer than a Grammar, but you want your child to go to the grammar?
When will it be considered? In the case of an 11+ fail, perhaps
at an Appeal. In the case of an application only to an Upper School, during Jan - Feb 2008 when the allocations are being made.
Does it make any difference? In the case of an 11+ fail for a GS, I doubt it. The evidence presented at an Appeal should demonstrate a child's ability, and has very, very little to do with parental preference.
For an Upper School, it is worth putting key reasons in that box, and attaching other evidence.
That is the key phrase - "we need documentary evidence".