My two cheeses in the cave are both 2 gallon makes and I can eat them in a single sitting.
It takes about the same time to cobble together a 4 gallon make as it does a 2 gallon. It makes sense to do the larger volume if you have the equipment and can afford the extra milk. The only times I would stray from that advice would be if you're just trying a new technique or recipe and just want to "test the waters". Certainly there are cheese styles that may be limited to a smaller volume of milk, such as Crottins, Pont l'Eveque, some blues, etc. Anyone doing a lactic using 4 gallons of milk will find that they have a huge
volume of curd to put into moulds. That's because there's no cooking or stirring to remove some of the whey.
Another very subjective consideration for a larger volume of milk is the end product...a substantial heft
when you turn it, wash it, brush it, rub it. You may say to yourself "Now, here
is a cheese!". While going through those actions with this particular cheese, you may envision the initial cutting and tasting...and maybe sharing with friends and family if it meets your stringent conditions of quality.
In a lot of cases a larger cheese will bring nuances that won't be available in a smaller version. What I'm thinking of is the firmer (or harder and drier) rind and then the softer, moister, beautiful paste inside. Consider the size of Emmentaler wheels that don't really develop their eyes effectively in smaller form factor versions.
The effort and resources that you devote to making and finishing this larger cheese ultimately reward you with a greater satisfaction for the job you have done.