When a commercial's expire date comes around, you would not want to erase that spot. Why? Because it would renumber all the other spots past it, decrementing them by one. You would have to maintain a list of spots and run dates, and when you needed to dub a new spot to one of the discs, you would have to first record it to the disc (making it track 51, let's say), then erase the old spot (cut 12), then perform a Move command moving track 51 to track 12. As you can see, this system could get a little hairy. Add to that the need to have the discs in the production room to do the dubbing when they need to be in the control room at the same time. This brings duplicate discs into the equation. Furthermore, if the log called to play spot 7 followed by spot 24 (which are on the same disc), you're going to have some dead air while you cue up cut 24 after 7 has played. Programmed playback is not available on the DN-990R (though it is available on consumer MD players).
Now, for things that aren't so "number" specific, the MD format is more attractive. For example, in the control room, the MD would nicely replace all the carts with jingles, IDs, sweepers, and promos. In many stations, this is well over 100 carts. The MD format can replace all those carts with one disc! As jingles, IDs, etc. are needed, they can easily be dialed up, not by number, but by track name, cued up within a couple of seconds, and ready for instant playback. Have a new promo going in? No problem, erase the old one and record the new one. As long as track numbers are not significant, the MD format is ideal for replacing carts.
The MD format could work well for music, too. The label on the outside of the MD could list contents and track numbers, or the disc could simply be inserted and scanned for titles and artist names. It doesn't make a lot of sense to transfer music from CD to MD if you have CD players in the control room, but for songs such as station edits, special mixes, oldies available only on vinyl, and things of this sort, the MD format is ideal once again.
Finally, who says the MiniDisc has to replace anything? The DN-990R is a beautiful 2-track digital recorder to have in the production room. Keep a "work disc" in the unit all the time. If you're in the middle of some heavy duty multi-track work, and someone comes in needing to record a quick voice-over, just press Record and drop the voice to the MD. You can retrieve it later for work on your multi-track when you're through with your other task. The 990R is perfect for recording multiple tags that need to go to cart. When through recording, it's a breeze to cue up to each tag as you dub it to cart. And when the 990R is not a fancy 2-track recorder, use it as a mass storage unit. Store all of your most used sound effects to disc, labeling each. Next time you need crowd noise, dial it up. No more fishing through SFX catalogues and loading up SFX CDs. Every time you go to a SFX library for an effect, record it to your MD for "next time." Do the same with often used music bedds. The MD format could also be used for mastering, but until MD is established in our studios, it might make more sense to master to a more common format, like DAT.