I can not express enough how important I think engagement pictures are for the couple and for the photographer! It is such a good opportunity for all parties involved to get comfortable with each other. Chances are you guys will end up exploring some new location together or just plain hanging out for a couple hours, and in that time personalities shine--the good and the bad:) In this little amount of time your photographer will also learn quite a bit about you two as well--for instance if there are certain angles you can't stand or if there is a hair that blew a certain way to watch for that in the future etc. This is also a great time to trial that spray tan and make up artist to see how you like it!
Now there is also 1 more reason why I LOVE engagement pictures... this is such a short special period of your life that is LIFE CHANGING--you two are choosing to spend the rest of your lives together and become 1. I love that aspect, and think it should be documented. Your madly in love and it is just the 2 of you. It is just such a special time and really it goes by in the blink of an eye. I think these pictures are the ones that your children and grand children will enjoy looking back on, and cause you to have those butterflies in your stomach remembering how it all began!