I agree that, like all things related to credit scoring, "it depends!"
On the positive side, there is little question that, from a purely computational point of view, increased CL will increase the demonimator in your % uti calculation. Thus, with all other things being equal, reduced % util is obtained.
However, on the negative side, requesting an increase in CL will almost always, in the consideration process, cause the creditor to pull your CR. Many code those requests for increased credit as a hard inquiry, which will, at least temporarily, lead to five-point-or so ding. Since that impact is short-lived, if you are not planning to actually app for new credit within the next six months or so, its immediate FICO impact will usually be worth the slight ding.
In my opinion, the most important factor is human nature. Many consumers, once obtaining a CLI, will consider it as more credit available to them, and will often quickly use up the new CLI benefit by increasing account balance until the % util is back near what it was without the CLI. If you use the CLI strictly for the purpose of reducing % util and refrain from a concurrent increase in account balance, it will be a long-term plus. The key is thus, in my opinion, not so much in getting the CLI, but in how you use it. Increased credit is not always desirable. Low balances are always desirable.
