I think walking or at least some kind of physical activity is essential. If you're already getting a lot of physical activity at work (standing, reaching, bending, light lifting, etc.) you don't need the extra activity of walking.
I've seen women in labor, who haven't had physical activity, and they can't even move their bodies from one labor position to another without assistance.
Unless you are placed on bedrest, you want to get good exercise so your muscles don't just atrophy. You've seen ladies who can't even get out of a chair unassisted in their last trimester - you don't want that.
Once you get further along you'll reach a point where you'll feel more energetic. If you can and are up to it walk and/or exercise. I was very active my 1st and it turned out well. I wasn't as active this time around but being older and to bend having a girl this time it's been different. Most important thing is to take care of yourself.
And my cousin didn't walk at all. She turned out to be huge, had a very hard time throughout her pregnancy, ended up having to get induced because she was so big and couldn't even sleep at night. She had to sleep sitting up on the couch.
All I do is walk. And I've gained maybe three pounds, healthy as can be, and I'm not big at all. I'll be 8 months next week and you'd think I'm only five.
Walking is not necessary. Just keeping healthy and looking after yourself is. I never walk at all really or very rarely and my baby is healthy and a normal pregnancy. Not sure why u think the walking is necessary. Best of luck with your pregnancy. :) xx