Full of use, advantage, or profit; producing, or having power to produce, good; serviceable for any end or object; helpful toward advancing any purpose; beneficial; profitable; advantageous; as, vessels and instruments useful in a family; books useful for improvement; useful knowledge; useful arts.
The trust of the innocent is the liar's most useful tool. Stephen King
A life spent making mistakes is not only more honorable, but more useful than a life spent doing nothing. George Bernard Shaw
Without reflection, we go blindly on our way, creating more unintended consequences, and failing to achieve anything useful. Margaret J. Wheatley
The production of too many useful things results in too many useless people. Karl Marx
Every man should make his son or daughter learn some useful trade or profession, so that in these days of changing fortunes of being rich today and poor tomorrow they may have something tangible to fall back upon. This provision might save many persons from misery, who by some unexpected turn of fortune have lost all their means. P. T. Barnum