Is it essential? Is it a waste of time? Does it even make a difference? The answer really depends on the person and the deadline. It is a combination of the way we react to a bit of pressure and if the deadline actually has significance to you emotionally, after all if it is just another Monday then what makes it special?
So, lets start with you as an individual. In general, deadlines are usually quite helpful in the right setting. Think of school assignments, sports events, EOFY, work project deadlines. Without a set point of completion things can just go on forever without anything being achieved. The same can be said for health and fitness goals. A deadline that means something to you can be a great tool for personal accountability. This has to be balanced with some self-awareness though. How do you respond to that kind of accountability/stress or pressure. Do you find hard to manage and resort to drastic tactics that may be unhealthy? Does it mess with your mental health to a point where you cant enjoy the process or celebrate the positive changes along the way? If so, a harsh deadline may not be the right approach for you. Extending it out and breaking the process up into small pieces may the optimal way go, ultimately it comes down to you and thinking about what is best for you. Another option is setting multiple forms of measurement for the same deadline, for example: A weight goal, a measurement goal and a clothing goal is a great combination for say, a bride to be. Lets say this person wants to lose 8kgs and fit their wedding dress. If they lose 5kgs but fit their dress and feel amazing in it then this 100% goal achieved. There are multiple ways to go about it.
If you are someone who works well with deadlines and finds that they give you a sense of urgency that helps keeps you on track then by all means use them. The trick with deadlines is making sure they are important to you at an emotional level, they need to be something you actually care about and will not easily forget. Without that connection it is just another date that will come and go.
There is a third piece to the deadline puzzle, and that is timeframe. I hope it goes without saying that setting a deadline of tomorrow for a goal that will take weeks is unrealistic. Consider how big your goal is, what your willing to do to achieve it and what your not willing to do/change. Is it a goal that will take at least a year to achieve in a healthy way? Is it something that can be ticked off in 6 months? Taking stock of these things and being clear on your answers (not what you think they should be but what they actually are) is crucial to setting up a realistic and reasonable deadline/goal date.
And there you have it, your three step guide to setting an effective deadline, or in some cases, not setting a deadline.
There is no right answer when it comes to the use of a deadline in health and fitness, there is only the right answer for you.