That's pretty much the biggest challenge of re-using an existing digitizer...cleanliness!
I guess it all depends on whether this is your device or not and how much you (or your customer) can tolerate dust and smudges. They're usually hard to see when the screen is brightly illuminated but totally obvious when dark.
If it's a customer device, then cleanliness is next to godliness IMO. Wipe it down with a micro-fibre cloth and if necessary, use one of those [https://carbonklean.com/product/screenklean/|square shaped lens pens]. They are the closest thing to magic :>).