No point in exposing the gas block. Makes it more susceptible to damage. Plus the majority of people tend to prefer long handguards that cover most of the barrel. Unless of course your 75 years old. Lol
The most important thing to protect is the fragile gas tube. The barrel and gas block as well but to a much lesser extent.
I'm of two minds on this latest trend. In some cases I do like the look. But I also like the look of the gas block on the end of the handguard. As long as the gas tube is protected, I think it looks good and with a rifle length gas system there is enough real estate for me to have a bipod, vertical grip etc. The added space is just more weight up front. On some of my rifles the handguard goes past the gas block and on others it doesn't. With newer stronger and lighter handguard designs they have been able to transition to longer handguards. However I would recommend being careful when picking your handguard if going past the gas block as some of them flex a bit and can start pushing against the gas block which doesn't help accuracy and could cause problems eventually.
With a carbine or even Mid length gas tube, I like the handguard to go past or just cover the front end of the gas block. With rifle length, I don't mind the handguard going to the back of the gas block. Especially with 308 rifles where you're looking at loosing as much weight from the front as you can.
Fighting guns where the gas block is exposed include: LMT MWS, KAC SR 25 (Pre URX 4), AR10t (Canadian military version), AR10 SASS, Scar 17 etc etc. Again, I'm of two minds on this.
As I said, I'm of two minds on this... Here's a SR 25 with 20" barrel. With the URX 3.1 handguard they protect the end of the gas block by shielding it from above. A carbine or mid length would be covered. Yet the URX 4 goes past. In the case of the SR 15 as seen below it goes past the gas block which is a midlength gas tube. While initially I wasn't sure about the URX 4 as the 3.1 I found more KAC iconic, I have to say, that I really do like it. With the lighter SR 15 it's actually fairly awesome.