When is it necessary to use a resistor?

(Sorry for all the silly questions as of late) So at the moment I'm working on various laser projects, and I was wondering when a 4.3 ohm resistor is necessary. I'm working on a 300mW infrared laser that has a Aixiz driver wired to the diode and before I fire it up (and possibly give it too much current) I'm asking if I'll need a resistor, or can I just go without? Any and all feedback is appreciated.

Dont use a infared laser for your first build. Use something of a visible wavelength. As for your question, since you are planning to use 808nm for your fist build, it is not necessary to answer it.

Well, I have a 405nm that I'd love to wire up, but I cannot figure out the pin configuration. It's a Sony SLD3235VF, if someone can help me figure out the pinning I'd be all for build one of those.

This should be the pinout for it.

As for your question, the aixiz driver current can be set. So there is no need for a resistor. Get a testload and you can set the current by turning the pot.