Pro (from my personal perspective, YMMV): You get to work on something that will actually see the light of day. For me, there's nothing worse than being this tiny little cog in the machine that comes into work from 9-5 and produces something so microscopic that you question your importance at all. Working at a startup means you have to pull your weight, wear many hats, and get shit done. This also means you can climb…
Working at a BigCorp(tm) right now, this is somewhat of a false statement imo, at least for us. Being in such a standardised place, it is very hard a lot of times to find new inspiration for technologies to adopt and things like conferences or meetups are the perfect opportunity to network and hear about how people make use of new things. Usually, we don't really get much time to explore new technologies as capacity is always planned for our current workloads. That's why I love being able to go to a conference every few months (this year it'll be 4 for me) to be able to bring some things back into my team that might be interesting to us.
We get the time approved for conferences, but not to explore things "while at work".
This obviously differs from company to company but that's my experience at my current one so far.