I'd zip them, always. If not zipped, falling could cause the jacket to ride up, resulting in rash.

It can be a bit tricky to reach around and get a grip on the zipper pull. What I did was put a metal round key ring on the zipper pull. That way, I can reach around and just hook my finger in the ring and pull. Made it way easier to get the jacket and pants zippered. If that doesn't work, attach something even a bit longer to the zipper pull.

 

I always zip up my Hein Gericke leathers and now textiles too :thumbup It's as easy as farting. First put the zipper together and then with one hand drag the zipper handle to the middle of your back. Once there, go with your other arm around your back and grab the handle and drag it back with your hand to your front. Then, just zip up the front of your jacket up to your chin and put the velcros together and it's done! As said, as easy as farting. :thumbup

EDIT: plus, as Honda said, if you don't do it, if you crash you could get major injuries to your middle, plus there will be wind chilling your exposed abdomen during riding and going up your jacket to chill the rest of your torso. Not pleasant during anything-but-hot days. Before I bought better textile pants I had to ride in cold weather with unzipped-together pants and short textile jacket.... was DAMN cold and unpleasant.

 

Lean the way the zipper slider is and do the ring thing mentioned above. WHEN you do crash eventually you'll lose a shitload of protection by not zipping - you'll be kicking yourself when the nurse uses a wire brush to get gravel out of your stomach skin.

 

try getting in/out of a 1 piece on a hot track day or a long day of weekend riding. Sometimes I wish I had a 2 piece LOL.