Just because you're newly single, doesn't mean you should jump back into the dating scene right away.
In fact, you may want to do just the opposite -- not date at all for a while. If you just got out of a long-term relationship with a partner, you need time to mourn the loss of that relationship before meeting new people, going out on dates and jumping into another relationship. When you go through a particularly brutal relationship that involved abuse or betrayal, take time from dating to heal and learn to trust the opposite sex again. Maybe you just broke up with a person but you're not over him yet. It would be unfair to date other people if you're still in love with someone else.
Dating takes a significant amount of time.
You have to find a person to date, plan the date, get ready for the date, then actually go on the date. To really get to know someone and find out if you're compatible, you need to spend a lot of time with that person. Career-driven people who spend 60 to 80 hours at the office don't have a lot of time for dating or anything else. Neither do people who work multiple jobs to make ends meet, raise children alone or care for a terminally ill family member. Sometimes you need to focus on only one area of your life and that's OK.
Self-discovery works best when you're not dating because it allows you to focus all your energy on yourself and not have to spread it around.
A self-discovery dating sabbatical allows you to work on low self-esteem, figure out what exactly you want out of life and a partner and reveals how fulfilling life can be without a partner. If you've only been attracting sleazy men or have a tendency to only date married or otherwise unavailable men, a dating sabbatical helps you understand and break those bad habits and destructive patterns.
Probably the best reason not to date is because you're already married.
You made a legal, social and spiritual commitment to be faithful to someone else. If you're unhappy or the marriage is not working out, either work on the marriage or get out of it before dating. Don't make your significant other one of those newly single people who need to heal before dating again, and don't be part of another person's bad dating pattern. Leave dating to single people.