They will usually be fairly different and that is normal.
“Balancing” the legs is ideal because it splits the load on the incoming supply from the Utility (or your solar supply) and the wires.
For most dual-phase (208/240V) devices the device itself will be using the supply in a perfectly balanced fashion between the phases. In some cases a 240V device can use ONE of the phases internally … e.g. a 120V fan in an otherwise-240V device like an AC unit. This leads to imbalance.
Imbalance also comes in the form of more 120V being used on one phase (leg) that the other. This is normally what you are seeing with the different wattages on each leg.
Unless you have a badly put together panel with, say, too many breakers on one phase, or lots of devices plugged into, by chance, one phase then generally houses are close to balanced (enough) that the imbalance makes no difference at the Utility level.
As a general rule, the more devices you have plugged in the more the power converges toward balanced. At the scale of the grid you can imagine things get very close on each phase.