We changed our policy a few years ago from 2 comps per cast/crew member to 2 comps that could be used only opening weekend. There was grumbling at first until people started asking around and realizing how few theaters give out comps at all.

By using them opening weekend (and we do grant exceptions), we paper the house in what would traditionally be the lightest time. We are able to get word out of the show's quality via word of mouth with these crowds. That advertising is still by far and a way our biggest draw (and our cheapest). Also, if we're going to sell out, traditionally it will be the final weekend, when (traditionally) is when most of our comp holders would show up. Since a paid ticket trumps a comp ticket, we keep the comp holders able to use their ticket. In the end, it made sense to everyone and they seem pretty happy with the system now.

We usually do 6 performance runs, 3 performances each of two weekends.  We have an invited dress rehearsal Thursday before opening on Friday.  Each volunteer gets two comps to that invited dress.    Volunteers include: on stage, back stage and front of house.  (yes, ushers see the show the night they volunteer, but concession people come to invited dress.  They miss part of the show because of working concession and cleaning up after intermission the night they are working later in the run)  We're taking a second look at the policy of two tickets for everyone on invited dress. But the original poster asked about perks, not tickets.  It seems like tickets is the only perk being talked about here.  We have an opening night reception.  Only cast and crew are invited along with donors & contributors.  People really like the opening night reception, it's a big deal, so that's a good perk.  Also, actors want a nice bio.  Some playbills or programs either have no bio's or they are one sentence or very short.  We have a nice playbill with good space dedicated for bio's and give them a small paragraph each and actors tell us they really like that.  We just make a playbill with more pages to make up for it and work hard to sell enough ad space to do that.  Many of our actors & crew like to party and socialize so we also usually have one or two people to throw a party at their house after a performance.  We also have a final strike party after the show is over with free food and drinks for the actors and crew.

At both theaters where I'm on the Board of Directors the Board throws an opening-night party for cast, crew, and members, and contributes to a closing-night party for cast, crew, and guests. At one theater (over 200 seats) anyone involved in a production gets two comps (but not for the best seats); at the other (70 seats) we give no comps BUT give honorary one-year memberships to first-time participants. Membership includes one comp ticket; the honorary memberships are given out at the closing party, which encourages participants in one show to come and see ANOTHER show. Also at the smaller theater we own the building, and we encourage cast and crew to bring snacks and beverages and relax together after EVERY performance and dress rehearsals. At the larger theater we don't have authority over the building and so cast and crew usually wind up going out together after shows, but this can become expensive. Both theaters encourage directors and/or producers to give gifts to cast and crew, but neither theater pays for these gifts.
At the smaller theater we also make sure that actors and tech people who have participated in a show get personal audition announcements for subsequent shows. We may be in the process of becoming able to do that at the other theater too. If the theater has a reputation for quality productions, being remembered and invited to participate in those productions ought to count as a perk.
I love the suggestion here of giving single comps to all auditioners. I find that actors who've auditioned rarely come to see the show if they haven't gotten the role; but a free ticket might encourage them, and they probably wouldn't want to come alone. Attending a show might also give them a clearer idea of what the director was looking for, and so would be educational.

I've worked with 3 different companies over the past year or so -- all have offered 2 comps, but I think I've only actually used one or two total.  I don't mind having the immediate family contribute to the sales, and I'd rather not have to make the hard choice among slightly more distant family and friends.

The times that I did use them were for former castmate friends who wouldn't have otherwise attended the show for financial reasons.  In one of the cases, the ticket price was something like $28, which can be a pretty big bite depending on your finances.