When I did "corporate" work I was often prompted to ensure that the marketing I was carrying out was on "on message" with central marketing strategy. I occasionally have the same reminder when working with some very traditional marketing agencies.
Marketing campaigns are targeted at specific demographics. That means that the look and feel of the marketing jigsaw needs to fit together seamlessly. The whole package of print, website, social media and face to face needs to give the same positive experience with no jarring when swapping platforms.
Social media isn't just about a demographic, it's about individuals too. Sometimes the people running the social media content need to have the flexibility to use their discretion. When you're dealing with an individual, the "standard" corporate approach isn't always appropriate. No matter how well thought out and planned your strategy is, it cannot fit everyone.
I always try and persuade managers that it's not only OK, but actually essential, to expect the social media person/team to occasionally veer "off message". I may have to start collecting pictures of the looks of alarm!
The objections are mostly down to a lack of trust in the abilities of the people delivering the content to judge the situation correctly. If you distrust their judgement that much then what on earth are they doing running your social media for you?
By all means issue pre-scripted responses to common problems, but trust the people you have put in charge of your online reputation to know when to be a human being. Better still, get someone to fix the problem so you don't have to keep addressing it.
Strategy is a necessary part of running a business, but sometimes you have to think outside of the jigsaw box!