In terms of percentage, how many times have been late on submitting your work to your employer?
I am proud that I have never missed any deadlines. The trick is time management and careful planning and build a buffer of about 10 to 15% for emergencies.
Guessing, I would say about 2%. I do try to give a buffer but sometimes problems still come up that cause me to miss a deadline.
In my case, I miss a deadline about once per week on one of my freelance jobs. It's a daily re-writing work. My employer doesn't mind though.
If the client is easy-going and not too particular to deadlines, I guess it is best to comply with the deadlines as a form of discipline and professionalism.