Most servos expect a 50Hz PWM signal, with the duty cycle varying from 7.5% to 12.5% for the two extreme positions. (Equivalently, a 20ms period, with 1.5ms ON for the extreme left position, 2ms for the middle, 2.5ms for the extreme right). (Yes, I know about PPM, but getting into that would confuse the OP without adding clarity).
Most servos are also pretty finicky on those timings. You can't just feed them a 7.5% duty-cycle signal at 1kHz and expect them to work.
So the answer really depends on what servo library you are using, and, of course, which particular arduino (or arduino-lookalike) board you are using, and whether you are using a dedicated servo driver chip. Some boards can only do PWM (pulse-width modulation) output by bit-banging, while some have hardware PWM output, and you usually set that by doing an analogWrite(). Even then, your particular processor may not support arbitrary PWM frequencies, and those it does may be too high for your servos. And since it's pretty hard to get really steady PWM output with bit-banging, you may end up in a situation where your servo is trembling, so to speak, around its target location.
The situation for a low-end processor (e.g., Digispark, or Trinket) may be even worse, as the serial/usb connection would definitely be bit-banged,and so would the PWM output. Or there may be a situation where the serial code is disabling interrupts and really interfering with the bit-banged pwm output.
i could go on forever. If you post your exact hardware setup, and what servo libraries you are using, I may be able to help you more.