I have seen many differing opinions on this from both professional and amateur chefs.
Some say seasoning before cooking starts to break the egg down and can make it a little watery. Others say season when mixing the eggs so the seasoning is well incorporated while cooking and better seasons the final dish.
Is there a better or worse to this or does it really not matter and just do whatever suits you?
I’ve done it both ways, at least in regards to salt, and find salting the eggs before cooking yields better results. I’m pretty sure I read this also in a place like Cooks Illustrated, as the conventional wisdom is to salt after.
Adding salt to the mixture does help break down proteins and keeps them from being rubbery. Other dry spices should be added in to the mixture before cooking; cheese or other fats should be added after it is in the pan but before the egg has firmed up. When I mix in vegetables such as onions, peppers, mushrooms, spinach, et cetera, I just sauté them directly in the pan and then mix in the eggs. Any sauces, uncooked vegetables and herbs, et cetera, should be added after it is plated.
Stranger
Just yesterday, I happened to be flipping through the April 2021 issue of Bon Appetit magazine and they had a double page of egg things.
Salt Before You Scramble
To ensure your eggs are uniformly seasoned and as soft and luscious as possible, add salt when you whisk them together, not when they’re in the pan or on your plate. According to food scientist J. Kenji Lopez-Alt, salt inhibits the proteins in the eggs from binding too tightly as they heat up, which means your scramble will have a moister, more tender curd and be less likely to weep (release water). In an ideal world, you’d incorporate salt 15 minutes before you start cooking so the granules can dissolve into the mix, but even a minute can make a difference.
I just consulted my copy of Salt, Fat, Acid, Heat. It’s got a table of when to salt certain foods; it puts scrabbled eggs in the “just before cooking” category.
If I am making bacon and eggs I like to sauté whatever veg I am using in the remaining bacon fat (I pour most off, of course) and then cook the eggs in that. I fear salting the eggs ahead of time would make them too salty.
An experiment is probably in order for me.
It just takes a pinch of salt; you don’t have to salt them to taste.
Stranger
I may be non-standard for this. Prior to making scrambled eggs or omelets, I take just off the boil water (electric kettle) and dissolve my salt as well as hydrate any dried herbs/spices (normally smoked paprika and red pepper flakes). While I get the rest of my mise set up, I let it cool until it’s warm, not hot, and then beat the eggs which I normally let get to near room temp prior to making the dish.
I find that I get a much more even distribution of the spices and salt, as well as less rubbery nature due to the reduced thermal shock that otherwise happens with fridge-temp eggs. Which I need, since by personal preference, I like my eggs every so slightly browned, which means overdone by all traditional standards. 
When I make scrambled, I season before cooking and beat the eggs thoroughly. My theory is that if I add the salt, etc. to unset eggs in the pan, there’s a chance that the seasoning will end up unevenly distributed, because the first time I stick a spatula in there, it’s going to slide to one side if it’s still atop a liquid. I use the spatula sparingly because I like the results to be a little wet, so I guess my theory would be moot if I were to do more mixing and mashing in the pan.
After decades of switching back and forth, I currently add salt before cooking eggs and pepper later in the process since the freshly cracked pepper looks better added later.