I have a little bit of experience with this now. So, I thought I'd post my results, so far. I haven't had much to work with besides Hulda Clark zappers, though (and they're not what other people have used; Hulda Clark zappers use specific frequencies with square waves and a positive offset; they usually are powered by 9v batteries; they're what I have; so, they're what I used; I imagine the results would be different with other forms of electricity).
My general, limited experience for live plants (and garlic bulbs) is that zapping them with a Hulda Clark zapper seems to stunt them for a good while, if anything. It doesn't seem to help cuttings root in water (although it does help the water stay looking good longer if you zap the water).
However, zapping seeds (in water) does not seem to have any ill effects, and in my experience, it seems to help clear the seeds of pathogens (e.g. anthracnose and alternaria). I've even experimented with seeds of infected fruits (I had Porter tomato fruit with anthracnose, and I grew it out after zapping and saw no anthracnose on the resulting fruit; I've done similar things with watermelon, but the plants seem to get foliar anthracnose, combined with spider mites, in my yard whether the seeds are infected or not; however, the zapped watermelon seeds whose parents have had it before have seemed at least a little more resilient than the others, with the exception of Red-seeded Citron, which was resilient from the start). I've been zapping seeds instead of fermenting them for a while now, and it seems to work, so far (that's my experience, anyway; this isn't exactly a full-on scientific study). I haven't noticed much, if any, effect on growth and production when I zap the seeds.
On a related note, I have found that exposing watermelon seeds to magnets seems to help them sprout a lot faster in colder temperatures (and there is at least one official study that speaks of improvements with exposing chickpea seeds to magnets—and while that's not electricity, it's not too far off). I did not notice faster germination in anything besides watermelon and muskmelons, however (muskmelons benefited slightly less than watermelons). I saw no difference in tomatoes, peppers, etc. I'm thinking the seed size, or iron content, may be important.
I think some of the benefit that comes from zapping seeds isn't directly from the electricity, however. I think the copper particles that get in the water from the copper electrodes (and hence probably in the seeds) may have an antimicrobial influence. I typically zap my seeds with a Z4EX for 15 minutes per each of three frequencies: 15hz, 2.5khz, and 30khz (usually in that order).
Zapping seeds also helps to dissolve plant matter that may be stuck to the seeds (but it's best to remove it beforehand).
Zapping seeds has not hurt germination for me. The seeds germinate quite well.
As for garlic bulbils, which aren't seeds, I think it's best to wait until they start growing some greens before planting them, if I zap them (like two or three months after zapping). I suspect the same would be true for seed potatoes (wait until they grow eyes). I can't say whether this removes diseases from such as garlic and potatoes, though. (I don't guarantee anything for seeds, either, but I suspect it works, at least for some diseases, with the procedure I mentioned—which honestly might be overkill.)
In summary, in my experience, it does seem that electricity (and definitely electromagnetic waves) can have some kind of influence on plants, both for good and ill. There do seem to be some practical uses for it for home gardeners, although my evidence for electricity is personal/anecdotal.