it helps with controlling the bike more easily/moving around on the bike and looking left/right/behind ect
thick stiff leathers make it harder imo,would be even more daunting having just passed your test/riding a bike
Well thats a load of bull

Leathers restrict movement off the bike, not on the bike, the cut is so that they aid in movement ON the bike, you don't see racers having problem controlling or moving around on the bike, I have commuted in a once piece for about 3 years and its never restricted me, the main issue is people buy poorly fitting leathers, its the same as helmets you have to try lots on to find the ones that fit you best.
Also the main thing on that is Leather are designed for sportsbikes, so if you aren't riding one the movement will be different, for that you should buy leathers that the supermoto guys use, they are cut in a way thats more comfortable sat upright, they have the double zips on the front for anyone interested.
Its a personal preference leathers or textile, personally I don't find textiles comfortable, the only thing I find uncomfortable are bike boots to walk in and they are going to be the same if you are wearing leathers or textiles.
If I have to do any walking I will pack some trainers in a bag and wear my two piece so I don't have to walk around like an idiot in a one piece.