I like to keep routing tables as clean as possible, and if your IP design and structure allows for very classful subnetting then there is no reason, I see to advertise all of your individual subnets when you could just have one aggregate address advertise out instead. Of course there are numerous reasons why you would not want this, route manipulation, etc.. but not in this case.
At this site my networks all fall into the 10.56.0.0/22 subnet.
As of now, my networks that are broadcasting to my BGP peer look like this:
The commands to enable route aggregation is listed below. What happens is that any networks within our aggregation block will stop advertising and in their place one summary route is added and advertised.
Now a get router info bgp will show that we went down from advertising 5 networks to advertising 2. This might not seem like a big deal, but if you had a large BGP network, with 100 sites like this, then aggregation can make a huge difference in router performance.