Programming at 8MHz vs. 16MHz clock speed

Hello,

I have an arduino nano and I've changed the clock speed from 16MHz to 8MHz to save power. The problem is that my code involves a distance sensor and millis() so it runs differently. In general, what things must be considered when programming at a slower clock speed like 8MHz for example?

Thank you

The bootloader baud rate is halved.

For everything else the best choice is to use a board entry with the correct clock speed.