IN_MEMORY=true settings question

[Oleg Ruchovets]

Hi ,
    Default value of IN_MEMORY is false. I am going to set IN_MEMORY to
true. Should it improve read operation and what is the trade off setting
IN_MEMORY to true ( We  use  hbase 0.90.4 (cloudera distribution)).  Where
can I read more details about IN_MEMORY settings. I  can't find any
information.

Thanks in advance
Oleg.