Perhaps a negative impact on the "time available to train"?
Surely an acceptable form of cross training though...
There's not much training you can do in 2 minutes.
Does that include warm up & cool down?
Organisation and structure of training.
This for me, partly down to wanting training to be flexible enough to fit in with everything else. This is a hobby at the end of the day, even though it might appear to be an obsession to an outsider. If I wanted to get a bit quicker at tri, I ought to book some swimming coaching.
Transitions are a big one for me too, as I lost 63 places in T1 at the Outlaw! 
I made up 83 places in T1, but that's mainly down to coming out of the water further back amongst folk that perhaps aren't so fussy about time as those 10 minutes ahead. In a sprint or Oly tri it might be a big deal, much less so at IM (unless you're chasing a Kona slot, I guess).