Thin seems to favor..."artistic endeavor". It shows skill on the part of the turner, and lightens the piece. There seems to be a preference for thin among many. I like pieces for display that are very thin, but if you are making products for actual use - you may want to temper that desire for thin bowls. They can be fragile if too thin and delicate to handle.
Thick is - for me - a sign of one or more things: the experience level of the turner. The wood itself - it may have some defects which were not discovered until the turning was well under way. Or an attempt to emulate an "industrial" or primitive style/look.
Woodturning has very few "rules" - other than safety in all we do. Safety first and safety last. Turn something, look at it, ask friends family and strangers to look at it. Ask for honest opinions. Look at as many pictures of classic pottery as you can. Observe modern sculptures. What appeals to you? Our eye is drawn to 2 things in particular: Graceful curves, and objects created which are mindful of the Golden Ratio. Or - practically, things that the design changes are made at a 1/3 or 2/3 of the length.
There are many rabbit holes one can go down in turning. Segmented, natural edge, hollow form, spindle turning, ad infinitum. Don't let it all overwhelm you. Pick something you like. Hang a picture of it where you can look at it while you are at the lathe - to refer to. And....have fun.