Bobbins and bite alarms

I've noticed that almost everyone who uses bite alarms also has a bobbin attatched and was wondering why this is? Why is it neccessary to have both?

Hello Rooster,
I am not an expert so don't take this a the perfect answer but I see it like this.
If a fish picks up your bait and swims towards you (drop back bite) and it takes the ledger with it no line will be pulled through your buzzer so no indication. But with a bobbin the weight of the bobbin will pull line back through the alarm giving the audible indication. You can ofcourse watch the bobbin and see the drop back bite without an alarm. I use a homemade bobbin which weighs just7g and is just enough weight to show a drop back without much weight for a fish to feel if moving away.
Also with the foot or so of line being taken before line is taken from the reel there is less resistance to the fish than line being pulled of the lightest setting on my bait runner! So if you set the hook before the bobbin hits the butt ring the fish hopefully might not eject the bait?
Hope this helps.
Neil.

when using 2 or 3 rods its a job to know which rod it is when you get a run but bobbins let you know at a glance which rod to hit.(not that i have ever hit the wrong rod, of course )