I've got to the point if the machine does not have one, and there exists a way for me to put one of those $2 inline filters on there, I do it. Most if not all of these smaller machines do have an in-tank one, but you know all it takes is ONE time that sob don't want to start and then you narrow it down to gunk in the carburetor, like I said, I got to the point for a buck or two, it never hurts to have one on there.
Not all machines will let you, most hand-helds are out of the question, but if there's a line and space, do it.
I order mine from J-Thomas, I think you have to order like 30 of them (or more) and the price goes down to like a dollar each, then if you order other stuff and enough to total over $300 you get free shipping.
Now I replace my inline filters once / year anymore, I just get tired of the down time.