It really depends what your purpose in delegating SP. I have received delegations from people as gifts with no timeframe and no specific instructions on how it is to be used {e.g. no self voting, no shit posts or posts that goes contrary to the beliefs of the delegator)

Some have shared with me delegation in order to help achieve better engagement and curation rewards. The added SP increases my bandwidth to be able to leave a lot of comments and share a lot of upvotes.

Fulltimegeek, Asher (abh12345) and the Stewards of Gondor was one such initiative that aimed to increase the engagement of the community and spreading the upvotes. Even though FTG is out fighting a war and had to get his SP, the people are still doing what they set out with and making Steem an engaged platform populated with people with a pay it forward attitude.

The Curation and Engagement Leagues - Sponsored by @carlgnash and @paulag!

You can also support people who care about the same things like you, like equality, morals, veganism, philosophy and psychology.

IMO 1 week is a two short time period to make a difference. At least 2 weeks to a month would have a greater effect.

In the case of size 100 SP is big for redfishes but may be lacking if the desire is more engagement, around 200-1000 would be your better unless the main reason is only to help the person get past bandwidth issues.

You can have it delegated to communities like newbieresteemday and promo-mentors who are doing their best to encourage people to stay and keep writing.

In the end it is your decision.