<p>I am building an enclosure for an Ender 3 Pro printer, and am planning on the power supply and LCD unit being outside the enclosure.  How important is it to move the printer controller (where the SD card is inserted) outside the enclosure?
Would leaving it in place affect its longevity?</p>
<p>Answers to the first round of comments/questions:</p>
<ul>
<li>I expect to be primarily printing in the 200C-270C range.</li>
<li>I'm not worried about losing heat from opening the doors - I'll be putting the SD card in prior to initiating printing.</li>
<li>I'm thinking the stepper motors are somewhat of a moot point, there's no way I could move them outside of the enclosure.</li>
<li>My printer is all stock.</li>
</ul>

It depends on what kinds of prints you make, and especially what kind of materials you want to use.
Certain materials (ABS especially, but also PETG to some degree) will print
much better
if the entire build area, which usually includes the printer chassis and controls, is enclosed to protect from drafts and allow a much higher ambient temperature.
If you print often with these materials, and the control board is included in that enclosed area, you
will
significantly reduce the life of the electronic components,
especially the capacitors on the board
1
.
On the other hand, if you print mainly with PLA, which is not as susceptible to issues requiring an enclosure, and prints better with an ambient temperature closer to room temperature, you can put the electronic controls wherever you want.
1 See especially this excerpt from the section on "Premature Failure":
Electrolytic capacitors that operate at a lower temperature can have a considerably longer lifespan.