I would like to offer a different perspective on performing benefits. In fact, I suggest that you strategically incorporate benefits into your tour plans every year. First, let me dispel the notion that playing a benefit means you play for free. That is simply not always the case. In reality, most organizations that attempt to use a concert as a means of raising money for their cause, are likely to select a performer with some recognition in the community, but not always.
Most notable performers charge a fee for their performance.
Sometimes it is their usual fee and other times they may lower their fee for the situation. If the cause is particularly important to the performer, they may donate back all or a portion of their fee. If the organization presenting the concert is a savvy presenter, they will seek sponsorships, donations and advertising to pay for most of the production expenses including the performer's fee. By finding sponsors to pay for these expenses, monies generated from ticket sales are then able to be used for the fundraising purpose originally intended by the organization, instead of paying for the expenses to present the event. In some cases, presenters may be inexperienced at seeking sponsors to offset expenses and will ask performers to play for free.