Mixing monitors from FOH means using one channel for two jobs – stage sound and FOH for the audience. This means sharing the same gain & EQ for both, which limits what you can do during the show.
On an analogue desk, using a Y-split can be really helpful, at least on the vocals, as this gives you separate channels for each job. On digital desks, you can split all the channels with ease – this leaves you with only the Gain being shared. But digital desks do have Digital Trim, which then allows further control over the gain of each channel.
Justin’s personal preference with the Drum Fill is to put the sub and top on separate mixes - this allows easy control of Low Frequency feedback without affecting the rest of the drummers mix. All channel processing on shared channels is audible in both monitors and FOH.
It’s preferable to NOT have compression on most instruments in monitors as this affects the way a musician plays – if it’s over-compressed, they will play harder and possibly “overplay”, which is not an ideal situation, so if you have a digital desk. It’s worth splitting as many channels as you can/need to.