Here is what the implications of "tightly balanced" means upon play:
1) Macro (at the overall conflict level and "workday" level, if the system involves such resources scheduling/recharge dynamics) play outcomes have a fairly high level of predictability for GMs.
2) Following from (1) above, GMs can enact mutivariate threats (conflicts with moving parts, stages, and/or short-term downstream effects) with consistent tactical depth (both GM-side and players'-side) and reliably avoid anticlimax.
3) Decision-points have a broad spectrum of action declarations that lead mechanical success.
4) Following from (3) above, a broader spectrum of action declarations leading to mechanical success means that more archetypes can put into action a positive gamestate change (achieving story-trajectory-impact-parity which emerges from gamestate change).