It is very common for clubs and organisations to ask members and non-members to support them through donations. Usually, this may be done by members giving cash in small amounts outside of any fundraising events that you may throw. This can sometimes make it hard to track - members may also want to donate but never have cash on them to do so meaning that the club miss out on their donations. Due to this feature though, they can now donate when paying their annual fees or at any time through the season/year.
Whether you want members to be able to make one off or regular donations, using this feature will enable those who want to donate to choose from a suggested amount put in by you or to put in an amount for themselves. The money can then be reconciled for you on the system, so you can see who has donated and what they donated.