Is it good general practice to avoid powering components from the 5v pin on an arduino?
For one specific use case, the answer is clearly yes.  Be very careful using the 5V pin if you power the Arduino from the USB port.  The internal regulator is bypassed via a diode which results in weird voltages appearing at the 5V pin. You will get some unspecified drop across the diode, especially if you're using a Chinese knock off as is common.  I measured only 4.72V at the 5V pin whilst the USB voltage was 5.11V. This can confound the unwary and cause unreliable operation of strict 5V kit.

It get's worse.  When the ADC is used in the normal mode, as in just reading it, you'll get errors.  The ADC references itself to Vcc which in this USB case might be 4.7V, not 5V. All your analogue readings will be  higher than you expect. You will have to mitigate by using either the internal 1.1V reference (if appropriate) or your own external reference.

So in summary, best practice would be independent external power if there is any remote possibility of USB operation. This doesn't mean a wall adaptor, but a power source external to the Arduino PCB itself.