Being a (long time) participant of MMMM, I have a lot of old seeds in my "try next year" pile. Instead of starting everything in soil, I've done a few soak (24 hour but can be longer ) tests to test for viability and re-hydrate the older seeds. I think I may have tossed seeds that were floaters needlessly.

While researching this topic, I encountered is a great deal of information on gastrointestinal issues. After passing those by, most postings were about cannabis, I'm starting herbs and some perennial flowers. I don't float tomato or pepper seeds, but maybe you do.

I soaked black eyed susan, parsley, and marjoram which are small and fragile. Some oldies but goodies are popping up after only 3 days, yay! But one variety of the black eyed susan is being stubborn. Guess that one is a gonner.

Curious as to what anyone usually presoaks, and for how long. When I presoak, I wait a few days to see if others catch up, brassicas especially. They germ all over the place for me.

- Lisa

I soak pepper seeds and I find it makes a big difference to how fast they come up. Helps with reviving older seeds too. I think you're right though, that the seed that floats is not necessarily a goner. I've seen some germinate, for sure.
I don't usually soak tomato seeds, but really old or stubborn ones I have tried it.
I do always soak peas before planting. There's no time to sprout like the present, when it comes to peas.
I've tried soaking parsley and celery, because they are said to have germination inhibitors, but they sure are awkward to handle after soaking.

Fresh pepper, pea, corn, and a few other seeds I presoak. Tomatoes if the seed is about a decade old, with the pinch of the blue stuff in the water. I sometimes do the same with old seed of other things, where I wouldn't presoak with fresh seed.

I discard floaters while cleaning fermenting tomato seeds. It's no big deal whether those would germinate or not, as it's usually about 1% of the seeds, and I save lots.

Because I grow peppers & tomatoes in a multi-year rotation, I am frequently starting seed that is 6-7 years old (especially now, when I am catching up after 2 bad years). I soak the planted seeds in their pots over-night, then pour off the excess water in the morning. It seams to help, the germination rates are usually decent.