Friends and colleagues want, and need, different things from each other -- They laid out four differences: friendships are voluntary, but you don’t choose your co-workers; friends relate to each other informally, but there are roles and power dynamics at work; friends spend time together to meet emotional goals, but co-workers have "instrumental goals," meaning they have to do their jobs; and there is no scorekeeping among friends, but workplace relationships are mostly transactional. These differences can lead to problems.
Friendships at work can harden into cliques
Social media makes it all public -- Seeing that co-workers went out without you, for instance, can be hurtful, and your co-workers can see the more candid things you share on social media than you would at work.
What’s work between friends? -- Workplace relationships can be affected by things like age, maturity level, gender, race, and level of seniority, along with the overall work environment.
Friends: they’re just like us -- You could end up competing with a friend at work for the same assignments, promotions, and resources.
(Quartz)