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there is a need to do so is the most popular phrase on the web.

it serves a a useful purpose 10 results on the web	there is a need to do so 118,500 results on the web More popular!
Some examples and use cases from the internet:	Some examples and use cases from the internet:
It doesn't look like this phrase is very popular! The search could not find any examples on the internet.	The second action happens when the first one does. Therefore, the second verb should be present as well. Change tense only when there is a need to do so. After the final version of a DBMS release is certified, Esri will test DBMS patches only when there is a need to do so. After it is determined that the DBMS patches�... ... themselves. Societies do, however, regulate professionals when there is a need to do so, through training standards, licensing and other requirements. To any content supply partner, where there is a need to do so, in order to supply you with a product of service you have requested. If we suspect that you or any�...

it serves a a useful purpose

10 results on the web

there is a need to do so

118,500 results on the web

More popular!

It doesn't look like this phrase is very popular! The search could not find any examples on the internet.

The second action happens when the first one does. Therefore, the second verb should be present as well. Change tense only when there is a need to do so.
After the final version of a DBMS release is certified, Esri will test DBMS patches only when there is a need to do so. After it is determined that the DBMS patches�...
... themselves. Societies do, however, regulate professionals when there is a need to do so, through training standards, licensing and other requirements.
To any content supply partner, where there is a need to do so, in order to supply you with a product of service you have requested. If we suspect that you or any�...