Performance is one of the key factors when considering pgbouncer in the first place. To make sure that performance stays high, some issues have to be taken seriously.
First of all it is recommended to make sure that all nodes participating in your setup are fairly close to each other. This greatly helps to reduce network roundtrip times and thus boosts performance. There is no point in reducing the overhead of calling fork() and paying for this gain with network time. Just as in most scenarios reducing network time and latency is definitely a huge asset.
Basically pgbouncer can be placed on a dedicated pgbouncer server, on the database node directly, or on the webserver. In general, it is recommended to avoid putting database infrastructure on the web server. If you have a larger setup, a dedicated server might be a good option.
One additional issue, which is often forgotten, is related to pooling itself: As we have stated already, the idea of pgbouncer is to speed up...