This is not true about laptop GPU's. Maybe a cheaper one, but my Alienware 17 with a gtx1070 was a beast hashing nearly as much as my 1080 back when I was using it to mine...  She is out of commission for the moment...turns out its very hard to keep something that small form factor cool. I am a jackass for using it so long to mine, The only way I would recommend it is if you could be in very cold temperature and keep the core or gpu temp at 70C Maybe 75C MAX. I would leave mine running 24/7 for up to a week at a time sometimes.... it would run at 90C sometimes, I deserved that one I guess... anyways.... don't like talking about my $3,500 paperweight 

sorry if I am resurrecting a dead post.