General pll question

[id31]

Hi all,
I used pic18lf46k22 at internal clock of 16mhz.
i have a specific code block that took long time.. so I used the setup oscillator to 64 MHz and all work well . After the block I return to 16mhz.
So my questions please:
1. Why not using 64mhz all the time? What are the disadvantages at pll?
2. Advantages/disadvantages at clk source internal vs external?

[Ttelmah]

The faster the chip is clocking, the more power it uses.
The maximum 'crystal' frequency of most chips is 25MHz, so anything above this has to use a PLL. Using a lower frequency clock outside the chip reduces RF noise compared to directly operating off the higher frequency, and also reduces the power requirements of the oscillator.

Internal saves two pins, and the cost of a crystal. Downside, not terribly accurate.

[id31]

Thank you!