Given that the usual ration is 100% : -100%, 50:50 is going to be helpful in escaping capability traps.
Ultimately, Google engineers can move between teams pretty freely, so if we allow a team to descend into an operational or a deadline-induced death march, and we don't address that quickly, chances are the engineers will move to another team. It's sometimes frustrating not to have more control as a manager, but it's a very nicely self correcting mechanism and fixes various incentives for us managers.
(I'm a manager in Google SRE. Not speaking for Google.)
My reference to "capability traps" wasn't accidental, it's a serious risk to any business where maintenance and improvement has low observability vs production outputs[0]. In that situation economists rightly predict that effort is skewed towards what can be observed more easily ("equal compensation principle")[1].
Under those conditions it's easier to fix a time-spent target and observe time allocated, even if only approximately.
[0] https://web.mit.edu/nelsonr/www/Repenning%3DSterman_CMR_su01...
[1] https://en.wikipedia.org/wiki/Principal%E2%80%93agent_proble...