I’m sure that with your first few Chao you kept repeating levels over and over again just to raise your Chao’s stats! Since you can only have 10 Chaos Drives or animals at a time, this becomes very repetitive.
It requires you to collect a maximum of 10 Chaos Drives and/or small animals within the levels of the main game, going into Chao World afterwards to give them to your Chao.
Raising your Chao’s stats normally can be a long and tiring task. Probably the most famous glitch in the game, and essential to know for quick, efficient Chao raising. Some are useful (some would say essential even!), and some are just quirky. There are a few glitches in the Sonic Adventure series relating to the Chao system.