I use Future a lot when working on my war gaming models. I use it as part of a mix to create what's know as "Magic Wash", a type of ink/wash effect. The Future does well to help seal and coat, but frankly I've found that Testors, Model Master, and even Krylon sealants are better for the purpose of sealing models.
For wet-transfer decals I use a touch of a brush on gloss coat, let it dry, apply decal and solvent/set, dry, they brush on gloss coat, dry, seal model.
For dry-transfer decals I have found that a heavy glossy surface can give some problems with the decals transferring over, sticking, or sliding.