I have several (4-6) different Google accounts, I use the Gmail addresses for different reasons and I forward the emails from all of them to a single Gmail account.
Occasionally, important messages in these various Gmail accounts will get mistakenly sent to spam (false positives). These messages do not get sent to my catch-all Gmail account. These false-positive messages are never critical (if they were, I'd choose to have them sent to my "main" account), but this has happened frequently enough that I wish there was a way to disable or bypass Gmail's spam filter so that every message comes through and the spam filtering only happens in one place.
If the spam filtering only happens in one place, I only have to check one place for false positives. Gmail's filters are excellent, but they're not perfect.