While you have your iron set up and other stuff, it is only a few more minutes to to do the other side. This makes a fuel proof, tight, seal, if your careful to seal the covering to itself. Sealing only one side takes care of the any escaping air through the gap, but does nothing to fuel proof or strengthen the hinge line, especially with CA hinges.

PS.........I have been building and flying RC for 38 years. Now this doesn't nessasarily mean anything. I could have been doing things wrong all these years, but in this case, I don't think so. I have never regretted taking the time to do something throughly, especially when it come to aviation.