What is MAX_BATCH ?
This is "hidden" parameter in <setup> section which controls how many oids can be placed in one single SNMP request when V2 or V3 is used in profile.
(*) V1 only support single oid in one SNMP request.
The default value is 20, so the probe places 20 oids maximum in one single SNMP request for V2 or V3 profile.
Take a look at wireshark image.
What is benefit ?
If you suspect the batch size causing issue most of your V2 or V3 devices, it helps to reduce the batch size in the probe globally.
What is side effect ?
Since this is global setting in the probe, the whole polling performance is expected to be slow down by lower number of MAX_BATCH.
If you set MAX_BATCH=1, technically speaking, it would be 20 times slower than default.
If you suspect the batch size is causing issue on specific devices only, try to use V1 for the specific devices only, rather than using MAX_BATCH.
Related KB.
SNMP service in Windows is known example unable to handle 20 oids at one request.
Reachability of Windows Host is showing as 0% in snmpcollector probe