I had one at so the doctor could get a baseline. I think it's a good idea. My little trick for avoiding that huge bottle of prep was to eat very little the day before the prep.
I cleaned out much faster :D I wouldn't worry about dehydration. As for what to do in 10 years?? I tend to think I won't worry about it unless I have any weird symptoms.If something runs in your family I think tests are the prudent way to go. I also think that we can over-test but it's not always the doc's fault. Malpractice suits have changed everything. Bottom line- it's up to you. Having said this I believe we must be responsible for our bodies and not rely on fate.
Glad you brought up this topic. Good luck!
Hugs, Sue RN