What are the pros and cons of sunscreen vs. protective clothing?
Clothing is a good choice for sun block while cycling. Unlike walking or standing still, there's always a breeze as long as you are pedaling which increases comfort. Long sleeves and long pants may be comfortable on a bike in hot weather even when they are uncomfortable indoors or walking outdoors. 

Pros for Sunscreen as sun protection while biking


It's invisible.
You can wear whatever you want.


Pros for clothing as sun protection while biking


Unlike sunscreen, it doesn't wear out after 80 minutes. You are never left wondering if it's time to re-apply or not.
While you may find that your sunscreen has run out half-way through a multi-hour ride (as I recently did), you are less likely to find yourself unexpected naked half-way through a ride. 
Regular clothing often has some amount of UV protection. While you might need to opt for full-coverage clothing, you don't necessarily need special clothing
Doesn't involve covering your skin in chemicals.
Don't have that covered-in-sunblock feeling at the end of a ride. 


Here's a photo of clothing-as-sunscreen before I departed with a friend on a 114 mile day on loaded touring bikes:



On a trip this past weekend I decided to spray-on sun-block instead. We I went to re-apply some half-way through the trip, I found the canister was empty. Sunblock-Fail.