Gyus,
Again, the checkpoint has nothing to deal with the size of the transaction, nor the log switch has. "active" redo log means that the redo log is currently being checkpointed and the checkpoint have still not completed, what ,yes, means that it's still needed for instance recovery, however no connection to the transaction size.
"If in case the redo size of a single transaction is greater than the total size of all the redo logs groups then most probable you will bump the "Checkpoint not complete" error."
That's simply not true. Checkpoint not completed is signalled when you are trying to reuse a log file, which is still not finished with the checkpoint and hence you cannot reuse it, so the server process have to wait until the checkpoint do not complete and the file is not ready for reusing. This appears generally when teh redo generation is faster than the checkpoint.
I am really amaized that such fundamental mechanism can cause such heated discussions.

Regards
Boris