A good letter of support from the sponsor is always worth while.
Many folks also provide for the child as well. Even though the applications may be linked it provides an opportunity to put into writing any key issues not previously covered.

There's no mandatory requirement for letters of support or letters of introduction..

With the onset of 'new rules', online applications and the streamined Manila Hub the value of the letters of support is an unknown, even if they actually get reviewed as a matter of course is not known.

It is however recognised as being an important benefit in those cases that fall for refusal and subsequent appeal. For that reason anything complex should be included.

There's not really any helpful templates as such letters are highly personalised and individual