Door sealing strip - what does it do/how big is it?

[schmokin1]

My chim has had a respray at some stage and is missing the strip on the door inside bottom face. I went to the Titt finish at the Ace cafe to have a look at a few other cars and none of them had it either!

Can any kind soul shed some light on where it should be, dimensions, and what it actually does? A photo or two would be much appreciated!

Cheers
Schmo