The right deadline can motivate staff, but it can be tricky to judge what’s appropriate. If it’s impossibly soon, employees can be demotivated and frustrated. Making it too generous can be as bad as not having any deadline, as it could encourage employees to go slow.
Of course, any deadline should reflect the actual needs of the business. As a manager, it’s important to bear in mind the psychological effects of setting a deadline. Importantly, you will be clearly communicating your expectations to your staff, which could impact their job satisfaction and productivity. You may also be increasing stress levels in the workplace, which can be a motivator for some staff but could result in burnout or sickness if overdone. You need to find a balance between getting things done quickly while also being manageable.
A good way of setting deadlines is in conjunction with your staff — ask them for input on timelines, giving them some ownership over the process.