if you only have one backup device, it doesn't make much difference in execution time, but if you have one big job, you have to search the job log to find the problem if the final status is "Failed" or "Completed with Exceptions"
I you have more than on backup device (eitehr more than one tape drive or multiple B2D folders), you can split the job to reduce the backup window
if you choose multiple jobs to one device, you need to make sure that the first job of the night is defined as OVERWRITE and the rest as APPEND, with all pointed to the same media set, and the media set cannot have OPP=0