Jalama,
It really depends on what you want the fly to do. Even a densly packed bug will eventually soak up water, and all the squeezing and false casting won't remove enough water to make the bug perform as it did without all that extra water weight. This can be good or bad, though, depending on what the fish want.
I 'waterproof' a lot of my deer hair bugs with permanent waterproofing liquid. The ones I treat like this float all day, never become waterloggged, and work as they were designed to do regardless of how long they are fished.
However, sometimes you want a little waterlogging. Nothing tied on the end of tippet makes the same 'sound' or moves the same way to attract a bass as a slightly waterlogged deer hair bug. I can't describe the sound, but the bass love it under certain conditions and I'd not venture out onto a bass pond of an evening without one available.
You can also do some 'fine tuning' with the whole waterproofing thing. I like the bodies on my frog patterns to float well, but I want the feather and hair tail to sink below the surface...so I waterproof the bodies but NOT the tails. After a few casts, the tails droop nicely while the bodies ride high.
Another 'partial' method that works as kind of a half measure is to coat the bottom of the bug with a light brushing of brush on CA glue. This seals the open ends of the densly packed belly hair, where 90% of any water will be soaked up through, and makes the bug float well but still get that bit of sloshy wetness that seems so effective at times.
So, if you find that the fish are hitting the bug well while it's 'fresh', but not so much as it gets some water in it, that's when you want a waterproofed bug. Conversely, if the bass are not coming to the bug until it gets a bit damp, then you fish one that's not waterproofed.
Good Luck!
Buddy
Long live the 'fuzzy bugger'!!!!!
It Just Doesn't Matter....