I think that really depends on the quantity you have and the area you could use them in. The best thing would likely be to work them into your compost if you have one going. I don't know the composition of spent brewers grains ( @RickCorey
) but someone here can probably investigate that for you.
If they are highly nitrogenous you could put them around heavy feeders, and mulch over them (which is what I do with alfalfa pellets for example). But "grains" makes me think maybe they are more carbonaceous and in that instance working them into the compost would be preferrable.
That's just my opinion, and a fairly uninformed one at that.