The frenulum is the most sensitive part of the underside of the penis, and most men say it is the most sensitive part of the penis of all. Sometimes it is still very sensitive after frenectomy, but usually it is much less sensitive. (And occasionally/rarely it's actually too sensitive after a frenectomy.)
Circumcision usually is not necessary because foreskin tightness can usually be corrected with gentle painless stretching over a period of weeks to months. It's pretty much only necessary to circumcise if it's the only way to prevent infections. But antifungal drugs, anti-inflammatory cream, and regular gentle painless stretching are probably a much better solution. You can always still get a circumcision in the future, but you may always wonder what it would be like if you had kept your foreskin once you circumcise (because you can't ever get it back).
Anyway, to answer your question, no it's not necessary to remove the frenulum, but if you have short frenulum, it may cause short ejaculation latency. You don't have to remove it even in that case. It can also be stretched slowly and gently over a long period of time. For more on stretching see the sticky thread Stretching To Fix Tight Foreskin (Phimosis).
There are some who doctors think having foreskin is a reason to circumcise, so don't let your doctor talk you into making a potentially bad decision without good reason. Circumcision reduces penile sensitivity by up to 75%. That's sensitivity men generally need with advancing age. The foreskin is most of the primary erogenous tissue of the penis. It's surprising how many doctors do not know that foreskin exists for a reason.
Incidentally, if you're having a problem with yeast infections (which can tighten the foreskin), cranberry is pretty good for minor yeast infections. Unsweetened is better. And milk and cream make it harder to overcome yeast problems, so it's important to avoid them if you're having trouble with yeast.
Last edited by mc7; 12-15-2012 at 05:16 PM.