The Sentry should always be used by the person with the best micro and best team skills. The most important part of your role is protecting others. The "Batman" builders.
An out of the egg level 1 titan does roughly around 115dmg with close to a 1 second attack speed. Walling the gold fully is a top priority for you at start. Even if you feel confident enough you can escape, it may not be the truth for all.
Upgrading walls at the gold early can buy tremendous time for those running plus your allies wood bases. Taking 5-6 seconds per wall is a very long time for 1 gold and 20xp. Buying 10-20 seconds per builder chase/recall adds up to a lot of undisturbed wood collecting time along with easier escapes.
---------------
"Fail walling" meaning leaving a 2x2 space or larger open, isn't necessarily fail if you have titan hunters such as Predators at the gold, they can act as a block, and also allow path in and out without wasting blinks and energy
This also allows Lurkers to enter and exit.
Just remember to create a large enough detour for those exiting
---------------
If you see an ally such as a Spectre who has minimal ability to protect their wood bases, help them out and give a warning wall. Don't be afraid to create random jukes... It might save a life later on.
The sentry should always be the top feeder on the board performing their duties as protector!
[/spoiler]
[/spoiler]