Some 120mm fans come with silicon pins to reduce noise and vibration.
Silicone "pins" is a bad use of terms. Some have rubber
isolation of one sort or another. Whether this is really
important has a lot to do with two factors:
1) Whether the fan is a good quality product or is poor and
imbalanced, thus more prone to transmit vibrations to the
case wall.
2) Whether the case itself has thin walls, and few folds,
such that any transmitted vibrations are likely to have any
significant effect.
Ideally, you will avoid both scenarios, having a fan with
low vibration and a case not very prone to transmitting
that.
However, are those pins enough to hold the fan and withstand the
temperatures inside the case? (about 40C) They seem very soft and make me
wonder how long will they last.
If made from the typical materials, they are fine in 40C
environments. They will last long enough, a more important
question is whether usign them sets the fan at a distance
from the case, even a few millimeters, which may interfere
with fan efficiency. If it interferes enough, you would
have been as well off just running the fan at lower RPM
without the insulator "pins".
Generally, with a good case and an optimal fan setup using
at least one 120mm exhaust fan, these silicon "pins" have no
real purpose, the difference in noise they reduce is less
than that of other parts in a typical system.