A variety of factors involved.
With the Auto brake providing a rate of deceleration, more reverse means less brake activity to achieve the same deceleration rate.
That means that brakes can be kept cooler, so there are no limitations on turnaround while waiting for brake cooling.
Especially useful if the turnaround is tight as seems often the case these days.
However, for noise abatement, some airports are now implementing the requirement of no reverse thrust to be used (unless necessary for safety reasons). This is often all day, not just night ops.
Therefore, autobrakes are providing the deceleration rate, Idle reverse being used as standard. That way any positive thrust is negated. I presume there is a small benefit in drag/ reverse flow, and they are deployed should everything go pear shaped.
on th B737NG autobrake 1,2,3,max,RTO
1 is lowest programmed deceleration rate.
3 is the highest programmed rate.
Max is the brakes driven to max available braking, protected by the antiskid.
RTO is obviously rejected takeoff.
The QRH has braking distances depending on brake selection.
As a guide, Brakes 1 or 2 seem most common for the majority of destinations we go to.
1 especially if the most appropriate turnoff is a long way down the runway. 2 if the most appriate turnoff is nearer.
Auto Brakes disabled by 60kt is common. Or if there is an overriding reason to control the brakes manually.