Light switch specs - max amps vs. watts
Power Factor
VA and Watt are sort-of the same, but not exactly. The difference is based on the power factor.
From a practical standpoint with residential lighting these days it makes little difference because with LEDs (and even with fluorescent), 600 Watts is a lot of light. On the one hand, with incandescent bulbs (a simple resistance load), the power factor is essentially 1, which is ideal, LEDs and fluorescent use so much less power that for typical residential usage this more than makes up for any power factor issues. It is easy to hit 600 Watts with incandescents - 10 x 60 or 6 x 100. But with LEDs, a 100 Watt equivalent might use 14 Watts, so it would take an awful lot of lighting on one switch to get even close to 600 VA or 600 Watts, no matter what the power factor.
In commercial settings the power factor becomes a real consideration as even LED lights can add up when you are lighting a warehouse or an auditorium or other large area. Large customers often have charges based partly on the power factor and may install equipment to improve the power factor. But that is not normally the case for residential customers.