Well as Muslims we always appreciate the help and support of another in trialing matters of this world so that itself is a big enough benefit. Be it in looking after kids, cooking and other household chores, taking care of you when you are ill,etc its always wonderful to have a friend and supporter who you can trust. Saying the husband can take leave is not possible...the lady was in hospital for nearly a month due to her illness and being a teacher her husband cannot just take leave that way. She has no relatives here in Qatar and do you realize how hard and expensive it is to find a person who will not only take care of all the household chores but also take care of the kids specially while the father is at work. Some of them are really small, mind you.
Besides all that its about how you feel personally. Some people find having a husband around all the time kind of stressful and actually appreciate the "me" time. On the flipside when you do like to spend quality time with your spouse away from the kids then you have someone to help you with that just as you would do the same.
Co wives can help and support one another in numerous ways. And for many of them who are away from their families their co wife is actually family to them and the love the companionship. Like one friend of mine who always missed her family is happy to have a co wife now who is her greatest confidant as well. These are things not everyone will agree with or understand but I do!
Personally I have no problem with my hubby taking another wife simply cos I know he does not belong to me and that by taking another wife he will not treat me with injustice or take away anything I've got,Inshallah,as he is not that sort of a man and that's why I'm married to him. And should he change and oppress me, God forbid, then I would leave him not because he married again but because he stopped been a good husband which can happen anytime.