Sequential downshifting is convenient if you're not sure when you'll get to quit braking. That way you're always in the right gear when it's time to accelerate again. Otherwise it's a waste of time and attention.
The only affect it can have on health of the transmission is if you're concerned about synchronizer wear. It shouldn't be a concern for most people but if you abuse yours then I guess you might try to make up for it when you can. In that case you would choose between 100% of the necessary wear on a single synchro or 120% of what's needed, spread over a few gears.
When you see racers doing all that clutch work, they may be double-clutching.
As for me, I throw it in neutral until I expect to accelerate again, then I choose the appropriate gear, rev-match before disengaging the clutch (effectively double-clutching), and it falls nicely into gear immediately.
im mainly concerned with an upcoming turn where i know what gear and speed i should be in
for other situations like a red light that may turn green before i reach it ill engage every gear just like u said
no i definitely dont abuse mine, it always slips into gear easily, aslong as im not downshifting 3 gears at a time at high speed without DC