Planning decisions are made on planning grounds, which are the local planning policy, regional planning policies and central government planning policies.
It is therefore important that you understand what is an issue that a Planning Officer can use as grounds in his decision and what is not.
For instance, the loss of a view from a window is not a ground for refusal but the loss of light or overshadowing is; an increase in the number of parked cars in an area is not a ground for refusal, but an issue of highway safety caused by the development is.
The Planning Officer has to use the planning policies currently in place to justify his decision or his recommendation to the Planning Committee in the planning report. So, if you have used the same policies to back up your reasons for your objections, it will give them greater weight.
It is possible that, despite your objection, the Planning Officer or the Planning Committee will decide to grant permission for the proposed development. It is therefore a good idea to think about this when you put in your comments, otherwise you will not have had any effect on the proposed development.
Say what you do like about the proposal, and what you think would improve it so that it would be more acceptable. This will not take away from your grounds for objection but it will make it more likely that changes may be made make the development better from the community's point of view.
Bristol City Council has a useful guide on responding to planning applications.