If you don't label tapes clearly and you don't have any record of where they have got to, it is not hard to imagine what can go wrong. If you have got one tape and you don't know what is on it you can take a quick look at it - assuming you have a Beta SP machine handy. No machine available and you are in trouble. If you have got twenty unidentified tapes to look at you're going to have waste/spend a day looking though them. If you have no idea where a particular tape is - and it hasn't been properly labelled - you are going to have a hard time finding it.