Hive LLAP mapjoin.hybridgrace.hashtable true = slower but safer processing

[#1]

We are benchmarking HDP 2.6.0.3 from our earlier 2.5.3. we noticed queries were running much slower and came across the mapjoin.hybridgrace.hashtable setting within LLAP. Changing this to false increased query speeds remarkably. The documentation mentions set it to true for slower but safer processing, false for faster processing. Can someone elaborate on the "slower but safer processing" note.

[#2]

The "slower but safer" comes from https://docs.hortonworks.com/HDPDocuments/HDP2/HDP-2.6.0/bk_hive-performance-tuning/content/ch_optim..., at the bottom of the page for mentioned configuration.