Generally it is safest to ensure that you have a current limiting resistor for LEDs. Diodes, once connected to voltages above their forward voltage, begin to draw lots of current. Red LEDs have lower forward voltages than blue LEDs. Know the danger - if your LED draws a lot of current it has the possibility of damaging the microcontroller pin that is driving it. You can decide whether that risk is acceptable for you. That being said I often do power LEDs directly.
My "rule of thumb" is that I always start with a 10k pull up/down resistor. It's more of a habit really. So when do I change that? It's all about timing (and sometimes impedance and *maybe* current limits). When restoring a line to the pull state the resistor will interact with capacitance on the line to form an RC circuit. A lower resistance will get you there faster (more current can flow through a smaller value resistor).
Too "weak" of a pull: Large value pull resistors may respond too slowly for you, and also don't handle any stray charges very well (they tend to stick around longer, imparting voltage in your line).
Too "strong" of a pull: Small value pull resistors respond quickly but can allow lots of current through (which could possibly damage supplying components). They also require the active portion (when the line is in the non-pull state) to provide more current so they can be a power waste. Finally, depending on the effective impedance of the current source they can begin interacting with the supply to form a voltage divider - in the non-pull state you might be fairly far off from the desired voltage.
https://learn.sparkfun.com/tutorials/di ... cteristics