also. more importantly, these will comtain the details of big show-stopping errors in the case of a crash or problems. A lot of Oracle errors such as the ORA-600s (internal errors) crop up in here. Most monitoring tools with check your alert log for errors such as deadlocks, archiver stuck etc..
Also, the reason the alert logs showed up in that location is because you did not specify your desired bdump directory location in the init file. That location is like the default place for your alert log files.