Of course you can put ground-up weed in a blunt. Would you expect to put a whole nug in a blunt and smoke it? Just curious, that's all.

If you get a good grinder, it will grind it up into mostly-even pieces. This means it all burns on the same level, for the most part. That along with rolling a good blunt means an even better blunt, or joint.

Yes, grinders are great. It's a lot quicker, too! And if you get one with a kief-catcher, after awhile you'll have some kief to sprinkle on the bud too. Or, if you let it go long enough, you could have enough to press and make into some hash. So yes, it's a good thing, with more than one possible benefit.