There's work and work. Most "tourist" visa will cover things like attending conferences or tradeshows, meetings with a different branch of your employer or customers etc, but on the other side more dedicated work, conference talks you are compensated for, ... can quickly be treated differently.

And if you don't come from a preferred part of the world even the former can quickly be quite a process to prove it.

Exactly. Being nervous, of a "suspicious" ethnicity, giving any indication that you're being paid for being in the country, can probably all lead to issues. As I wrote elsewhere, aside from some countries that require a visa for any explicit business activity, a basic visa is typically fine to go to a conference or meet with a customer, much less send some emails.