In my market I have found that for the most part, working with renters is a huge waste of time. Prospective renters get very flaky, and usually in addition to working with an agent, they'll also be looking on craigslist and other free or paid services that have homes not listed on the MLS. So you do just as much upfront work as in sales, but with less odds of closing anything, and for a tiny commission that barely covers your gas.
However - having said that, I will work with higher end leases on a case by case basis (either tenants or listings), if I see something to gain from it outside of the lease itself. For example it's a great way to meet new people who can potentially refer you, and people who lease do end up buying or selling (I have a deal in escrow right now that came from someone who I originally found a lease for last year). But I am very picky about these and I will fire the client very quickly if they seem wishy-washy or flaky, or I don't see any gain from getting to know them as people or spending time with them. It's just not worth the aggravation....