Pros
The quality of the engineers and PMs that you interact with daily are really what makes Twitter so awesome. Great people build great infrastructure which frees everybody up to work on more impactful and interesting projects rather than endlessly debugging issues. Also, working with talented engineers ensures that you're learning something new every day which makes career grow a natural consequence of the job.
Cons
It's hard work and there is a lot of pressure on all the employees to deliver products on short timelines, it's sometimes hard to strike an appropriate work-life balance. Also, the constant stream of new product asks have pushed back efforts on paying down technical debt. A number of the acquisitions we have made were not worth the exorbitant sums we paid for them, IMO.