"Having the right go-to-market plan to achieve revenue strategies is critical and almost always, one of the elements of a successful integration." - Massimo Malizia.
Every plan has a direct impact on people. Try and translate what's on paper into real life. It might be immediate or in the long run, but any changes are guaranteed to impact people's lives.
There are two major challenges regarding GTM integration:
1. sales team retention
The sales team will suffer massive disruption if synergies rely on full integration.
2. legacy customers
These customers might have long contracts to honor, so you have to keep selling and supporting them for a long time using the legacy system.