It doesn't matter how many years you've been designing, we all need to iterate to get closer to perfection. The more times you can iterate, the better, but we all have time limitations, so we need to be fast at designing - and thats where workflow comes in.
These UI kits provide you with a huge amount of pre-made UI elements which you can just drag and drop on your page. To find them, open figma and go into the figma community on the top left. Then search for the following (I'll add in links later if I get time):