The conversion to UTC will lose the original local time so you cannot retrieve it once time zone data changes, unless you perform reconversions every time you detect such a change in tzdata. And countries changing time zones happens more often than we think (and also on short notice).
Thus it is important to distinguish between instants (e.g. for recording when exactly something happened after the fact) and wall clock time (e.g. for coordinating people and goods at a certain place, like meetings, concerts, departure times). For the former use UTC, for the latter use a localised time zone (e.g. Europe/Rome), not an offset time zone (e.g. not +0200).
For more information Jon Skeet has written about this multiple times.