The question is a little confusing, however, Paraguard is a medicine, so in that respect it is certainly useful. I don't think I'd just starting treating every fish that comes in with Paraguard, but certainly it'd be a great multi-medicine for quarantine tanks. Some people probably treat all new fish, but that seems a little wasteful to me. The reviews out there are positive, and Seachem doesn't sell junk, so I'm sure it's a good product.
Just like any medicine, it has its uses.
It's probably a little pricier than your standard ich treatment, but since it's a multi use thing, it's probably nice for when you don't fully know what's wrong.
So I guess I'm answering your question in two parts: Part 1: Medicines are useful and Part 2: Seachem makes good products and the reviews for this specific product are positive.