Margarine/butter new tub question

[cpheonix]

Apologies if this sounds like a silly question, but when you buy a new tub of butter/margarine, are you meant to leave the additional piece of paper on top of it all the time (that's under the lid)? Is it meant to be more hygienic or keep it fresher somehow? Or do you discard it as soon as its opened?

[Lakitu]

I discard mine as soon as I open it (unless I need to grease up a tin). I haven't ever considered keeping to be honest.

What do you do?

[jack daniels]

I've always binned it but my in-laws leave it in (don't know why)
I find it gets in the way.

[cpheonix]

I discard mine too but i know a few people who leave it. It does get in the way which is why I've never understood why people leave it, hence asking this question. I always thought there's some reason behind it rather then just laziness!

[heathfield]

If you leave butter (and some spreads) lying around unwrapped, you'll notice them becoming a darker shade of yellow. This is due to an oxidisation process that leads to the butter (or spread) eventually turning rancid. Exposure to light helps this process, and is the reason that most butter comes wrapped in aluminium foil, so as to make the packaging lightproof. Since it's not a good idea to have butter in direct contact with aluminium, a bonded layer of greaseproof paper is used to keep them separated.
If you want butter and spreads to stay fresh for as long as possible, you'd keep them covered with the original wrapping.

[Lakitu]

But if it has that peel off bit, then it's in a tub, which has a lid so it needn't be exposed to air or light?