Why would I do this?
To better protect the strut from road debris, and hoping to prolong its service life.
Just make sure the dust protector can breathe.
Yes, strut BELLOWS need to breathe. The strut itself, no. If the bellows had no bellow on it from the factory, don’t put one on. You won’t like the results if you do.
I seriously doubt that would add any longevity to strut life. I’d leave them alone.
You don’t say…
Make?
Model?
Model-Year?
What kind of roads do you drive?
Do you wear out struts, regularly? What’s the average longevity, now?
I have never replaced struts on any car I’ve owned (GM & Chrysler), and only one broken spring (actually replaced the pair… coil over strut) on an 82 Dodge Aries. Also, I keep my cars beyond 200,000 miles. The struts themselves on my cars just don’t wear out, they’re fine, no zip-ties, no"longevity" issues.
However, I have worn out and replaced a few strut top bearings/bushings/cushions that have developed rattles. (A bad strut bearing probably caused the broken spring.) That would be the time to replace struts for somebody who thinks the car needs them and wants to waste some money.
CSA
It may hold moisture in. I have never heard of anyone doing this, but myself think it is not needed.