It takes power to run locomotives. It takes no power at all to run tracks, because they don't do anything by themselves. So, most of what the power pack needs to do is run engines. If you can put 2 locos on the same track and run them, then you can probably put the same 2 locos on different tracks and run them.
There are a few other considerations, though. If your track loops are very long, then there will be "voltage drop" from one side to the other. You can help this a lot by installing multiple feeders to get the power to the track more efficiently. Rail joiners are OK for power distribution, but with time they will loosen up, and they too will cause voltage to drop from one side to the other. Again, more feeders is the answer, and soldering the feeders to the rails is the best way to avoid problems with rail joiners for power. The typical way of doing this is to use a heavy gauge wire (#12 or #14) as a "track bus" beneath the layout, running out from the power supply, and then thinner wires (#20 or #22) from the bus to the track.
If you have illuminated passenger cars, they'll also draw power from the track. Be aware of this, because it can sneak up on you as you add more of them to your layout.
If you're using the same power pack to drive your electrically-operated turnouts, then you may notice a brief drop in engine performance when you throw the turnout. Likewise, if you're using it for structure lighting, streetlights, etc., each of these will draw a bit of power away from running the locomotives. You are really better off with a separate power supply for everything other than your track.