Planning and agility are often seen as opposites. However, as a recent HBR article (https://goo.gl/wMpCnD) explains, both are necessary.
Taking the HBR article a bit further, it is really a question of balance, and that balance is dictated by the following factors:
Task - relative importance and complexity, time available, etc.
Team as a whole - capabilities, composition, maturity, etc.
Individuals - development needs, etc.
Wider environment - corporate culture, senior stakeholder interest, etc.
The good leader can flex his/her style and devise processes appropriate to the situation's needs.