Free blog hosts owner have to pay the bills and earn few bucks so he redirects your mobile traffic and puts his ads, sometimes quite a lot of them - that sucks in terms of money making and search engine traffic (redirects/cloaking/etc...).
I've made nice money with Thumblogger/Sensualwriter, but that time is over. Google algorithm's changed, free hosted blogs get shitty to none traffic - it's better to spend that time building blogs on your own network. It's cheaper, it's safer and bring much more $$$ making opportunities
I still build some auto blogs on free blog hosts here and there, but it's like few % of my network and it should stay like that.