Personally, I never assign tasks to developers, nor do I tolerate pm/po/seniors/leads assigning tasks to others. Developers pick their own tasks, and coach the team as a whole to ensure that the way tasks are divided encourage learning and collaboration.

Juniors only picking “safe” tasks or seniors taking the juicy tasks is seen as a team dysfunction. I can see how random assignment might help a team break out of negative habits, but in general I prefer to just talk about this with the team, help them become aware (usually they already are, just not talking about it) and allow them to take responsibility for their own functioning. Assigning tasks, even at random, is the opposite of self-organizing.

The key to any of this is psychological safety within the team. Team members should be free to address things like some people hogging certain tasks, or others apparently afraid to pick up new challenges.

In such a culture, seniors will openly encourage juniors to pick certain tasks (“let’s work on that together, you can learn some new stuff”) and juniors will feel free to pick things they have no experience with (“I wanna do this one, who can help me with that?”). Seeing such exchanges happen is one of the things I really love about managing developers.