It's a pretty vague (and slightly strange) question, but I'll assume you mean why do we still need them?
The most obvious use of a single penny is in the oft used 99p, £4.99 and £9.99 price tags.
Most people will round it up in their heads, but will still stand there waiting for their 1p change.
If the penny is discontinued, will retailers round it up to the next pound, or still try to use the psychological ploy of making it look like a pound cheaper by using 98p instead? If you follow that on to it's next logical conclusion and assume the 2p goes too, do we then get 95p shops instead of the glut of pound shops that exist now?
There's already a 99p shop in my neck of the woods and they must use 1p coins by the barrow load, although I suspect some people decline the change as useless thus adding a nice bit of extra profit to the store. 1p might be insignificant to you, but times the hundreds possibly thousands over the course of a day, could go towards paying one of the staffs wages.
I see kids chucking copper coins as worthless trash quite often, but you only need to keep a jar or tin somewhere and then use one of those automatic changer machines you see in a lot of supermarkets to see it's not worthless. I recently cashed in my (mostly) copper coins and got £14 - you wouldn't throw £14 on the floor would you? And that was only about three weeks worth, so multiply that to a years worth and it's clear to see the humble penny is not insignificant at all.
No, it depends on what the penny has been trough ex:a 2008 penny will weigh more than a 1980 penny because the 1980 penny would be wore down over time causing it to weigh less then a 2008 penny
The cast of Family Court with Judge Penny - 2008 includes: Penny Brown Reynolds as herself
The cast of Penny - 2008 includes: Victor Burke as Mark Pascal Scott as Finbar
Penny Rigden died in 20 August 2008 of cancer.
2008
Shatner's Raw Nerve - 2008 Penny Marshall was released on: USA: 2011
Family Court with Judge Penny was created in 2008.
The Penny Dreadfuls Present... was created on 2008-01-11.
The cast of A Pretty Penny - 2008 includes: Max Cullen as Roy Firth Chris Haywood as Jack
The Mighty B - 2008 Penny Hearts Joey 1-11 was released on: USA: 26 June 2008
$1,000,000,000,000
2.5 g