Be friendly with your employees, but don’t be friends with them.
To be effective, managers need to to be obliging when they can and tough when they must. The boss-employee relationship implies a power structure that makes managing friends quite challenging. It can be difficult to give objective performance feedback to your friends, convince them defer to your authority over them, or to decline requests for specific allowances without harming the friendship.
Few managers who’ve been promoted from within to manage their peers come out of the boss-employee relationship with their friendships intact.
If you decide to be friends with your employees, don’t do it at the expense of being a boss.