I have heard some people say that to make the best bread, you should use little yeast, and let the dough rise for a long time (about 24h). However, I am wondering if you can achieve the same results by just putting more yeast in the beginning, and rising it for only several hours. Chemically I don't see what the difference would be.
Yes, there is a lot of difference. In principle, having food prepared under different conditions while keeping some total variable the same, tend to have different outcomes - having the same outcome would be the exception, not the rule.
Yeast colonies live and metabolise differently under different circumstances - imagine how people live in the Icelandic countryside and in Hong Kong, something similar happens to your yeast.
What is most pertinent to the taste are some compounds which get built in hot, overcrowded conditions (a quick rise), but not in the slow ones. These are most notably ammonia and thiols, and some people experience them as too harsh in taste. Also, if you do a low and slow rise, you get a tiny bit of lactic and acetic acid formation, as in sourdough. During a slow rise, the texture also changes, with extra gluten formation through autolyse.
The current trend is for artisan breads to do slow rises and to have the flavor profile from retarded doughs. Quickly risen breads have a homemade quality to them, and are not perceived as very refined. It is up to you which one you prefer.
I think the difference has to do with fermentation - more fermentation, more flavor. When you are relying mostly on yeast for the rise over a short period of time, flavor that stems from fermentation doesn't really have time to develop. Less yeast + more time leads to more fermentation, more flavor. More yeast + less time leads to rising but without fermentation, hence less flavor.