i rolled my first joint yesterday (im usually a blunt person but i didn't have a wrap or enough weed) and out of curiousity i decided to add a bit of my menthol tobacco to it and HOLY mother of jesus it worked well for me. i swear the hit was stronger, it wasn't clean(kind of harsh in my opinion) but i felt myself getting higher by the second. Lasted quite a bit too.
i talked to a brit friend and he says everyone over there does it bc the weed is much stronger there and you have to kind of "dilute" it, in a sense.