if you plan on doing any serious freestyle it is infinetly advantageous. I cant stand trials unis for freestyle 
ive got a 20" standard uni and a 24" MUni. when doing freestyle i find that the 20" is a lot better for doing most tricks. It is a lot easier to do flip tricks and i found a great difference in SIF and hopping. I figured it is because of the size of the wheel, a lot more torque and it is a lot lighter.
Maybe we will see some Freestyle/Trail hybrid unis in the future?
The german shop ajata.de already offers a special streetstyle uni ( http://www.ajata.de/ratshop/offerdetails.php?id_offer=227&from=offers ). Personally I thing 125mm cranks might be an advantage for freestyle and streetstyle tricks (smoother handling and lighter wheel). The best hybrid tire might be something like a 20" x 2,25" slick on a good freestyle rim.