It varies as you say with individual airlines. Blinds down in the cruise at high altitude often depends on the whim of individual passengers rather than an airline policy. Hot sun streaming through a window can be downright annoying especially to some one trying to sleep.
In most Australian airlines, I believe it is company policy to have the blinds up for take off and landing for the reason you gave. But you then get the ridiculous situation at 15,000 ft on descent the flight attendants walk up the cabin and tell you to raise the blinds when there is at least 20 minutes to go before landing. The blazing sun hits you through the window and you feel blinded by the glare. All the FA's have to do is ask passengers to raise the blinds when the gear goes down for landing..
One Pacific airline I flew on had the FA's turning off all the cabin lights in daylight during take off and descent for perceived ease of night adaption even though it was midday. There are some crazy inexplicable policies around often dependent on the intellectual ability of officials manning the safety department of the airline. And worse still is where you get a bolshie senior flight attendant interpreting company policy his/her way and they just love the power.