Are BOGOF's frugal?

I went to the vets yesterday to pick up some flea treatment for the cat and dog. When I got home I discovered that the flea treatment must be on a BOGOF. Woooohooo, I thought, free flea treatment. Just what a froogle lover like me wants or is it. Problem with this is that when my six month old border collie takes her next growth spurt she'll be under-covered and I'll be left with flea treatment that I don't need.

So this got me thinking about BOGOF offers and are they frugal or are they just a big con. I know some are fab, like buy one toilet roll get one free or buy one chocolate bar get on free. But there are some rather silly ones, take food for instance. If you live on your own do you relay want the BOGOF cucumber? Would it not be better for them to offer the cucumber at half price, saves money and proberly waste. What I've also noticed is that it makes me want to buy things I don't relay like or need. Take Eco products they never seem to be on offer but the big branded goods do. So the froogle side of me wants to buy them but the greenie in me screams nnnnnnoooooooo. At the end of the day the greenie always wins but it does get you thinking that maybe this is just another way to get you sucked into buying all the things that you relay don't need.