Hiring strategies like this are often used as a legal pretext for paying women less than men. Economists call this the 'marriage monopsony.'
The idea is that because men on average earn more money, or at least did until recently, women generally move when their husbands get a new job. This means that men are able to compete for the best wages in a global market, but women are only able to compete for the best wages in their local market. Which, depending on their industry, often means only a handful of options, and thus severely limited bargaining power.
until recently, women generally move when their husbands get a new job
In academia we usually refer to this as the "two-body problem". It sometimes results in a spouse earning less because they can't negotiate as effectively; on the other hand, it also often results in a spouse being hired who wouldn't otherwise have been. Statements like "I'd love to work here, but my husband will need to find a job too... can you hire him as a lecturer?" are far from uncommon.
The idea is that because men on average earn more money, or at least did until recently, women generally move when their husbands get a new job. This means that men are able to compete for the best wages in a global market, but women are only able to compete for the best wages in their local market. Which, depending on their industry, often means only a handful of options, and thus severely limited bargaining power.
See also:
http://econpapers.repec.org/paper/izaizadps/dp7343.htm
reply