Sorry, that was quite a vague question indeed. :) I deleted some stuff from what i had originally typed, and didn't check what was left after that.
I have a programming background and really like doing stuff in max with js, but i am indeed wondering if i should use it for time sensitive stuff. I am worried that any issues will not be very noticeable, and that later on it might just be 'somewhat not in sync'. I am planning to make a beat-slicer/reshuffler, where i intend to have groups of samples that have a chance of being played on a certain step in a sequence. So all i'm doing in js will be doing some random selections in arrays, resulting in an index of the sample to be played, which will be converted to a message to line~ so the correct part of the full sample will be played. This all will be triggered by the beat, so probably from a metro. This isnt all too much in js, but maybe someone advices against any use of timesensitive js at all, no matter what you do.
I could be wrong about this, so someone please correct me if I am, but I think everything running through js ends up in the deferred que in Max6. This makes triggering events by running a call through js less than timing-accurate. Array manipulation is incredibly handy, but you might want to send the manipulated arrays out to [coll], and then trigger the data via [metro] (e.g.) so that things happen immediately.
I tend to use js these days for UI and scripting inside patchers (it's great for that!), but leave all the heavy lifting to native Max objects, java, or gen~. Resultant values can always be fed to pattrs, whose value can be retrieved in the js using this.patcher.getnamed('whatever').getvalueof().