What id difference between email tracking and email tagging in crm 2013?

Hello all,

We find that following internal query getting executed more frequently during initial business hours.

(@ModifiedOn0 datetime,@PartyId0 uniqueidentifier)
SELECT DISTINCT top 51 "email0".ModifiedOn as "modifiedon" , "email0".MessageId as "messageid" , "email0".ActivityId as "activityid" , "email0".RegardingObjectId as "regardingobjectid" , "email0".Subject as "subject" , "email0".RegardingObjectIdYomiName as "regardingobjectidyominame" , "email0".RegardingObjectIdName as "regardingobjectidname" , "email0".RegardingObjectTypeCode as "regardingobjecttypecode"

FROM Email as "email0" JOIN ActivityParty as "activityparty1" ON ("email0".ActivityId = "activityparty1".ActivityId
AND (("activityparty1".PartyId = @PartyId0)))

WHERE (( "email0".ModifiedOn >= @ModifiedOn0
AND "email0".MessageId is not null))
ORDER BY "email0".MessageId asc ,
"email0".ActivityId asc

I found following useful blog which mentions the reason of frequent execution of this query.

https://community.dynamics.com/crm/b/dynamicscrmsupportblog/archive/2012/10/11/crm-e-mail-tracking-part-3-tagging.aspx

My questions are,

1) What is the actual use of this query?

2) What is difference between email tracking and email tagging?

3) What will be impact if we disable email tagging option from all users? Note that, We are not using email router in our implementation. Is it possible to disable for all users through some server settings?

4) Will this query executes frequently during normal business hours also? If yes, then do we have any settings to change interval of execution of this process?