I've only encountered one situation when weather sealing was (very) useful.
I was in the mountains shooting landscapes and tiny critters with my father.
Back then, I had a Pentax K10D + Pentax DA* 16-50 f2.8. Body and lens were both weather sealed.
My father had a K10D + Sigma 17-70 f2.8-4.5. Only the body was weather sealed.
There was a bit of pollen in the air from pine trees. We didn't really pay attention and kept shooting without taking any special precaution as the pollen was not so noticeable anyway.
Later on at home, my father changed lens. The inside of his camera was... yellow! Tons of pollen had gotten inside. He had to send the camera back to Pentax to be fully cleaned.
On the other hand, my camera inside was spotless.
These days, I almost exclusively use non-sealed Fuji bodies and lenses. I often go on vacation to the beach as we do quite a bit of kitesurfing. Taking kitesurfing pics or the kids at the beach, even in very windy condition, I've never encountered any issue with sand or water. Of course, I'm careful with my gear but I don't use bags or anything.
As to shooting in the rain, it probably never occurs (or rarely) unless you're a pro that must be shooting regardless of the weather condition.
I was in the mountains shooting landscapes and tiny critters with my father.
Back then, I had a Pentax K10D + Pentax DA* 16-50 f2.8. Body and lens were both weather sealed.
My father had a K10D + Sigma 17-70 f2.8-4.5. Only the body was weather sealed.
There was a bit of pollen in the air from pine trees. We didn't really pay attention and kept shooting without taking any special precaution as the pollen was not so noticeable anyway.
Later on at home, my father changed lens. The inside of his camera was... yellow! Tons of pollen had gotten inside. He had to send the camera back to Pentax to be fully cleaned.
On the other hand, my camera inside was spotless.
These days, I almost exclusively use non-sealed Fuji bodies and lenses. I often go on vacation to the beach as we do quite a bit of kitesurfing. Taking kitesurfing pics or the kids at the beach, even in very windy condition, I've never encountered any issue with sand or water. Of course, I'm careful with my gear but I don't use bags or anything.
As to shooting in the rain, it probably never occurs (or rarely) unless you're a pro that must be shooting regardless of the weather condition.