Auto-tagging appends a unique ID to the end of the destination URL. This unique ID allows Analytics to report the details of the click: which AdWords keywords brought a visitor to your site, which campaign that keyword was from, and how much that click cost. If there is a redirect on a link, this will cause the unique ID parameter to be removed and Analytics wont know where the visits came from, so due to this the analytics data is less.

2. GA IS A STANDALONE
PRODUCT
GOOGLE SAYS “Google Analytics is a
standalone Google product that shows you data
about your visitors – how many visitors are
coming to your website, where they’re coming
from, what pages they're seeing, how long
they're staying, and where they go when they
leave. With advanced features, you can even see
what paths people are taking to get from certain
pages to other pages.”
http://support.google.com/adwords/bin/answer.py?hl=en&answer=2404031&topic=1714059&path=1713967&ctx=leftnav

3. EVEN ADWORDS NEED
TO BE LINKED TO GA
GOOGLE’S TWO DIFFERENT PRODUCTS ADWORDS
AND GOOGLE ANALYTICS NEED TO LINKED
BEFORE THE CLICKS CAN BE TRACKED PROPERLY.
GOOGLE SAYS “Linking a Google Analytics account
to your AdWords account can help you analyze
where people who click on your ads go once they
reach your website. This information can help you
improve your ads and your website to try and make
more money per click.”

4. GOOGLE SAYS ADWORDS
MATRICS DON’T MATCH GA
AdWords increments Goals the same way regardless of
whether you are using the 'native' AdWords conversion
tracking code or are importing a Goal from Google
Analytics as an AdWords conversion action. In either
case, we do not expect the number of google/cpc Goals or
Transactions in Google Analytics to exactly match up with
the number of Goals or Transactions reported in the
AdWords interface
http://support.google.com/analytics/bin/answer.py?hl=en&answer=2679221

5. DFP DOES NOT MATCH
GA
EVEN DFP MAY NOT MATCH GA
WHEREAS A PUBLISHER WHOSE SITE SERVES
CERTAIN # OF ADS ON A PARTICULAR PAGE
THE PAGE VIEWS EVEN DON’T MATCH THE GA
PAGE VIEWS
http://support.google.com/dfp_premium/bin/answer.py?hl=en&answer=177405

6. STANDARD NOTE
Auto-tagging appends a unique ID to the end of the destination
URL.
This unique ID allows Analytics to report the details of the click:
which AdWords keywords brought a visitor to your site, which
campaign that keyword was from, and how much that click cost.
If there is a redirect on a link, this will cause the unique ID
parameter to be removed and Analytics wont know where the
visits came from, so due to this the analytics data is less.

7. OTHER REASONS
If a visitor clicks on your ad and then gets redirected to another page, the
auto-tagged parameter that identifies a visit as coming from NETWORK gets
removed from the URL.
A visitor may click your ad multiple times. When one person clicks on one
advertisement multiple times in the same session, NETWORK will record
multiple clicks while Analytics recognizes the separate pageviews as one visit.
A visitor may click on your advertisement, but prevent the page from fully
loading by navigating to another page or by pressing their browser’s Stop
button. In this case, the Analytics tracking code is unable to execute and send
tracking data to the Google servers. However, network will still register a click.
If a visitor who clicks on your ad has either JavaScript or cookies disabled,
this visitor won’t be recorded in Analytics, but the network will still register a
click.

8. CONCLUSION
CLICKS RECORDED IN GA UNDER VDOPIA DOMAIN MAY NOT BE
THE ONLY CLICKS WE SEND
OUR CLICKS MAY GET RECORDED UNDER OTHER NAMES OR
THROUGH WEDSITE URLs
OUR CLICKS CAN ALSO BE RECORDED UNDER UNIDENTIFIED REF
URLs (the urls from were traffic comes to your site)
GA can tell you your traffic but can never exactly tell where it came
from.
If there is a redirect on a link, this will cause the unique ID
parameter to be removed and Analytics wont know where the visits
came from, so due to this the analytics data is less.