seat configuration

Airbus A320 has max 189 seat in all economy class. But Some player configures less seat than all economy like 20c 140y. 20*1.6+140=172, so just have 172 seat.
Why they configures like that?
What is good point of that? This question's answer is just range?

Some people prefer to play the game a bit more realistically & use seating configurations that are more commonly seen or at least somewhat plausible (I usually do 16C 132Y, which is close, but not identical to what Air Canada uses). I don't want to imagine how cramped a 189 seat A320 would be. I'd rather not make an airline that cramps PAX in that tightly...

Others prefer to opt for a 3 class seating setup that mirrors the average demand ratios, but still take up as much space in the plane as they can. This can work well if you're playing to win because the extra money you can make on the F & C class seats can offset the reduced amount of total pax; especially on routes where there is a lot of Y competition so the fares are low. I can't remember the exact ratio (because I don't bother with these setups), but it's something like 7C seats per F seat & 7Y seats per C seat. Just look at a normal route demand graph & you'll figure it out. Is it necessarily better than an all Y class configuration? Maybe not, but I think that depends on the route & your competition on that route.