logo:Porgs were cute and not as annoying as ewoks but also served no purpose - same with BB-9E. 

Apparently the Porgs exist because they needed something to cover up all the hundreds of Puffins on Skellig Michael,

and it was easier to digitally paint over the puffins rather than removing them all and then blending in new backgrounds to replace the digital cut outs....

http://www.nme.com/news/film/star-wars-the-last-jedi-porgs-origin-debut-puffins-2182100