Local numbers can send MMS which Toll-free numbers aren't capable of. Some users place an MMS coupon in their messages where local numbers have an advantage. However, MMS are rarely used as Contactreach's digital coupons aren't used in this scenario anymore. In that case, coupon redemptions cannot be tracked nor the coupons' value. 

On the other hand, Toll-free numbers cannot send MMS. But the good thing is customers can call these numbers completely free of charge. This is extremely beneficial for campaigns that are IVR-enabled.  More info about IVR here.