any problems from blades (wet over time)?
There can be yes -- potentially it can be very bad for your blade over time... but it depends a lot on the species of wood in your handle, in the blade itself, and the amount of sweat you produce.
All timber 'moves' to a certain degree -- by this I mean that all wood works like a kitchen sponge -- it has the potential to absorb moisture either from the air (or in this case your hands) and swell up in size in the process, just like a kitchen sponge.
This moisture is then lost as the wood dries out, and the wood shrinks again. This can in some cases cause warping or cupping in the wood as well (or other similar defects).
It is impossible to stop wood moving without completely encasing it in something like solid epoxy. All sealants like varnish, shellac, PU etc ever do is slow the process down to the point we don't notice. Different woods move different amounts, and absorb/ lose water at different rates.
If your hands sweaty a LOT, and the handle isn't sealed, then the excess moisture can soak into the handle scales, causing them to swell up, and get thicker. If it's a flexy blade, this has the potential to alter the way your blade flexes, and by extension, alter the throw angle (only the tiniest amount mind you, but still potentially enough to alter the ball's landing point on the other side of the table by a significant amount.
Wet wood also rots / degrades quicker, so you're not going to get as much life out of a blade.
Worst of all though, water will 'wick' along the full length of a piece of wood, given enough time and moisture. This moisture can then (theoretically / potentially) also then start moving into any other piece of dry wood that's touching the wetter wood. (Glue can slow this down or potentially stop it in some places, but only if that glue is impervious to water, and many types of wood glue arent. Through this mechanism, the average moisture content of your entire blade has the potential to change.
Furthermore, really sweaty hands + unsealed handle scales can cause problems with your outer veneers degrading over time, **especially if the end grain of the outer veneer is getting wet at the base and sides of the handle.**
If this happens, water can slowly wick up and through the wood, eventually reaching the playing surface. If this happens it doesn't really matter if you seal the playing surface or not, it's going to suffer some water damage anyway, as your handle sweat will wick up through the timber *underneath* the sealant, basically white-anting it from the inside out.
Granted, this is all a very slow process. For all of this to happen quickly, you'd need to basically be soaking the handle in a bucket of water for several hours a day... But if you hand sweats enough, and if you play often enough for your handle to costtantly be wet for several hours a week, then water damage to your blade is not exactly going to be a slow process either.
Long story short -- to extend your blade's lifetime and preserve its throw angle, always seal your handles. This won't stop the process, but it will slow it down a lot, to the point you get a decent life out of your blade. If you don't like Polyurethane on your handles, try a drying-oil based sealant instead eg: linseed oil or Osmo oil.
(NB: for further info on the various effects of excess moisture on dried wood, google the term "what is wood movement in carpentry, and how do you deal with it?").
