Risks and Benefits of Choosing a Smaller Chastity Cage?

Several sizing guides I’ve come across suggest that the cage length should be about a quarter to half an inch shorter than your fully flaccid measurement. I’ve had good results using this rule of thumb. However, browsing online reveals many nano and micro cages that are roughly half my total flaccid length. This raises two questions: (1) What do you gain by compressing the member significantly more than what is needed for proper alignment with the end opening? And (2) Are there any long-term downsides, such as atrophy or circulation issues, from this heavy compression of a flaccid member? Thanks.