In particular, at the beginning of a campaign and after any changes (i.e. creatives, etc.), are made an exchange will validate the creative with a bot/creative validator.
Note: In the Targeting dashboard these validator clicks/visits are filtered out of reporting.
How can I filter these bots/validators in my Analytics?
The exchange tags the URL with a query parameter of "bw-preview=1"
This appended parameter signifies that the visit was from a bot/validator and serves as a potential filter to use within your own analytics.