Is using a breaker as a switch damaging to the equipment or to the breaker?
Both a breaker and a switch accomplish the same task when manually switched off. They break the positive wire going to the equipment to stop power. Both have the same effect on equipment.
Switches and breakers will wear down a bit every time they are used. However, quality equipment will last many, many cycles. For example, looking at the blue sea breaker specs shows they are rated for 10,000 cycles (turning on or off). So even if you turned the breaker off or on everyday, it should still last over 25 years.
I would still recommend first turning equipment such as chartplotters, radars, etc. off by its own power button/switch (if it has one) before turning off breakers.