Not everyone is an expert on relationships; often it's through person-to-person contact and experience that you learn from your mistakes and realize why taking things slow in a relationship is beneficial to its success. There are exceptions to the rule, however, and people choose to take things slow for different reasons.
Love and Respect
When someone is attracted to you and has feelings for you, they tend to be more methodical in their approach to dating. The courtesy of taking it slow is for your benefit -- it's an attempt to let things develop on your end and wait until you reach their level of mutual feelings or attraction. The idea is to enjoy that stage of love and really relish in it. Taking things slow in this case is a good thing because it shows maturity on the individual's behalf and respect for you as their partner.
A Guarded Heart
If a previous relationship didn't end well and the individual got hurt, naturally, that person is going to be more cautious the next time around. They're going to take it slow because they haven't figured out yet what your true intentions are in the current relationship; you have to earn their trust first. While it’s fun to lose yourself in someone else for a while, if you do it too long, you increase the danger of losing yourself altogether, or at least that's how guarded individuals see things, explains mental health expert, John Grohol, Psy.D., in his article, "5 Things Not to Do in Your New Relationship."
Unsure Where Things Are Going
Sometimes the individual likes you as a person, but isn't sure if the feelings are there, so they take things slow in the relationship to see if anything develops. Generally, this is the case when two friends feel a connection and want to see if they'd be a good fit for each other, romantically. The opportunity of reverting back to a friendship, if things don't work out, is more likely when taking the relationship slow.
Fulfillment and Lasting Relationships
Many couples rush into having sex too soon and take the next step without looking objectively at the odds of the relationship succeeding, says University of Massachusetts, Amherst, psychology professor Susan Krauss Whitbourne. In her "Psychology Today" article, "Take It Slow If You Want Your Relationship to Last," Whitbourne stresses the importance of waiting to have sex, as having sex too soon in the relationship often leads to moving in together too soon. She says that many of these "hurried unions" have less satisfying relationships, resulting in breakups.