Well you can have a total load of up to 1200W on any of the 4 channels, but you cannot exceed 2400W in total.
You could put 2x 300W on each
channel or 1x 500W/600W on each channel, or
You could put 1x 1000W on one channel and then 1x 500W/600W on two of the other channels, or
You could put 1x 1000W on two channels,
and so on and so forth.
Basically, as long as you stay within the max load per channel and max load overall, you will be ok.
Some of the smaller 4 pac dimmers that I have are a total load of 2400W (we are 240V here) per channel and overall. So, I can link all my lights onto one channel or I can balance them out over all 4. Can get a little confusing but calculating your loads (and being able to convert that into
amps) is a good habit to get into, especially if you are using
distro boards. That is a subject for another post however.
Hope thais is helpful.