Mic or go direct is a good question and the answer is not a simple one. Is this live or for recording? What sound are you trying to capture? What do you consider is part of your signal chain? Acoustic or electric guitar? So many questions… Let’s get started.
I answered a post on the Telecaster Discussion Page Reissue recently on this topic and I want to expand on that topic here. I don’t like to give long explanations in responses to posts as I don’t think they get read completely. It is more of a short answer format, in my opinion. Anyway, here we go:
What are you trying to capture?
A backup question may be, what do you consider to be part of your sound and signal chain? If your speaker is part of the sound, then you would be wise to grab a mic. You may have a small amplifier with a sound that you feel really conveys your music, this will need a mic in some larger venues or even when recorded. If your speaker is really nothing more than just amplification of everything else up to that point, then go direct and save yourself the hassle.
However, a complicating factor is whether you will have some sort of monitor, either a fold back speaker or in-ear monitor. If you cannot hear yourself, all bets are off. You obviously will not mic a monitor but the hassle of bringing an amp for yourself can be mitigated if a monitor is available.
Live or recording?
The same question applies as above about what you consider your signal chain and sound. However, there may be other options to consider when in the studio. For example, how about a little of both?
You can add some dimension to your guitar parts by mixing in direct with the miked speaker. Just like adding an acoustic guitar to an electric part (and vice versa) can add some depth and definition, adding a direct recorded guitar can add that one thing that seems to be missing. I will do that with my acoustic. Piezo undersaddle pickups are not my favorite but have a place in my recordings occasionally. The dynamic response and frequency range can add a missing element if not used front and center in the mix.
There are numerous examples from the Beatles to today of plugging in an electric directly into the console. Reverb has a nice article titled 8 Famous Guitar Tones That Were Recorded Straight Into the Board. This is with and without guitar pedals!
Acoustic or electric?
You could say I have already answered this but the question of live versus recording definitely influences this decision. Acoustics have the nasty habit of feeding back terribly when live and loud. There are ways of dealing with that and going direct is step #1. In the studio, it is just the opposite. You want as much of the natural sound of the guitar as possible as the main signal. Mic the guitar with a good condenser as if you were recording vocals and it will sound great.
Electrics assume you are going with a speaker as the design naturally minimizes unwanted feedback. Especially if you play a solid body, you have the most control over the feedback (ala Jimi Hendrix). These days with modeling software, the need for an amp is reduced or eliminated. I use Amplitube from IK Multimedia and in-ear monitors when I play live in my church. The sound guys and I get along much better and I can play the most outrageously loud cranked amp in my collection with abandon!
Mic or go direct take-away
The take-away here is: Think about the needs both of your sound and the venue (including the recording studio). It is good to try some of both now so you can get a feel for what they sound like under various conditions. You may surprise yourself and change your mind several times. Try before you buy, right?