i've used 'bottom line' a few times- i like the thinner threads in the bobbin- sure saves winding bobbins so often-especially if you are working on a large project and don't want to have to stop to wind another bobbin.
it depends on the machine though- and i guess what thread you are using on the top- once in awhile i have to change thread a couple times to find the right combination- if i'm not matching threads.