It really depends on how you want to use MIDI tiome code. MTC by itself is in fact a "poor man's time code", because, it is in fact tied to MIDI clock, which isn't super accurate, even though at 96 ticks per quarter note can get you there, the whole point surrounding MIDI is music production. The initial applications for MIDI were to remotely control other devices by providng a common signalling protocol. Later on as sequencing became more and more a reality via hardware sequencers(at first) and there came a need to have clocking in the sequencer, MTC began to be a requirement. Later on with computer sequencing and more requirements, MTC began to really become essential, but only as something that worked off a SMPTE time code, with interfaces doing a SMTPE to MTC conversion.
With MyDMX, TRUE sound trigger is impossible as there is no interface for it. Then, well, why not implement a sound to MIDI trigger device? Because that device will feed the converter box and output the same MIDI note time and time again, so it's not practical for MyDMX, considering most people want to do the old type of "chase" that you use with hardware controllers.
Even so, with SMTPE, SMTPE CAN drift, which is why it's a lot better to use SMTPE with digital sources as it will greatly reduce drift. This drift is largely due to analog recording of SMTPE time code, which while accurate, can be "smudged and smeared" a little bit. Tape can stretch, warp, deteriorate and even wear out. With digital, you do avoid some if not all of those issues depending on how you're working with it.
Still, SMTPE to MTC sycn will still be subject to some degree of drift. It is generally recommended to work in short time amounts, say, roughly 15 minutes, which is I think what film makers call a "reel". As SMTPE to MTC improves AND as digital non-linear workstations are improving and as recording tactics change and revert back to older tactics, these limitations are starting to ease back.
For example, if I were working on a film and am slaved to SMTPE, I'd keep my synth tracks and other MIDI tracks as MIDI until the very end in order to preserve as much as possible until final mixdown. MIDI won't wear because you never recorded anything to tape. But we're not recording to tape anymore, or are we?(I love analog 2", but I'd rather track to that for certain things then bounce to ProTools). No, these days, the MIDI sequences aren't being used as they were before. The MIDI tracks are being submixed(the audio being produced) and are then being dumped to digital audio tracks, and the dragged into the production or timeline. I find this to be foolish because songs can change or evolve and you don't want to commit to that until you absolutely have to.
MyDMX simply does not respond to MTC, period. So, while you may have timed everything to work perfect with this one tempo, MyDMX doesn't have the capability of tempo mapping. MyDMX works off "hard time", or what the actual time is. It is not dynamic. If you need to speed or slow things up or down, you have to get in there and manually tweak values. This is a deliberate limitation of the software. You don't get those sort of goodies until you step up to higher end products. Not bashing MyDMX in any way, but folks who need a lot of really tight syncing and the ability of time expansion and compression really shouldn't be using MyDMX because as good as the product is, it's not the right product for that sort of job. MyDMX is more for the DJ/small companies who want computer control over lighting in an easy to use package. And for that, it does the job amazingly well.
MyDMX still has tons of things in it, and is great value for the money. MyDMX isn't limited to the boring chases of the past, unless I'm your lighting designer, since my shows tend to be rather "boring". You can make chases, but the chase system isn't handled the same was as a hardware controller where you can bump it along via a sound trigger. If you think more scene-based chasing, you can say "do this scene, then do that scene" and repeat until you run out of scenes, and you can't repeat scenes without it starting the pattern over again, which may not necessarily be a bad thing.
Chases in MyDMX can be as simple as a series of simple scenes strung together, or it could be more multi-step scenes strung togehter, or if you really want to think outside the box, it can just be one way complex mega scene with hundreds or thousands of steps within it.