What started off as a four note chord would be smeared out a little by MIDI, especially in the early days until everyone worked out that putting MIDI for an entire studio down a single cable was a bad idea.

Then you'd get some more smearing in the target synth CPU as the incoming notes were parsed. Then perhaps some more delay for each notes, because it took a while to send trigger and pitch messages to the hardware. Even more if there were if there were software envelopes involved and they had to be initialised.

This is still a problem with VSTs, on a smaller scale. There's some finite amount of processing that has to be done before sound starts being generated. Usually it's not very much, but there's always the possibility that two notes that should start in the same 5ms buffer slot will be spread across two of them because one note is just a little too late.

This isn't as objectionable as glitching, but it can still affect the timing feel, and - depending on the patch design - cause phasing effects between the notes.