I see a lot of comments and debates related to things other philosophers said. I see value in reading and learning what others have written and think. I am not suggesting that such an exercise does not help. However, it seems that constantly turning to others for the answer is a crutch, and that too much of such behavior causes one to be more of a historian memorizing who said what. As I think about this I start to wonder if history could be categorized as a philosophy. I also believe in giving credit where credit is due, and so it makes sense to provide references at times. Is it necessary to study history to be a philosopher? Or, can we deduce things ourselves and let philosophy be an activity?
history is there to analyse records of the past: what happened, when, where and (perhaps) why. it asks questions that can be answered by researching documents and other traces of the past.
philosophy asks different questions - about being, values, consciousness, etc. it goes back to its own history of asking this kind of questions in order to build on the answers it accumulated so far, trying to avoid those answers that proved to be wrong or lead nowhere.
you can memorize who said what but that does not give you answers to these questions, at least not in a helpful/meaningful/concrete way.
Ironically, it can be harder to think original thoughts without being steeped in the history of philosophy. Older philosophers' concepts have often become so deeply embedded in our collective worldviews, that unless you go back to the source, it might never even occur to you that you could think a different way.
To put it another way, you can tell how great a philosopher is by counting how many people have found it important to refute what he (or she) said. It's comparatively rare for a philosopher to expound at length about agreeing with a prior philosopher --new work is generally phrased as an improvement at best, and more often as a refutation and replacement.
As far as history in general, we all benefit from studying it (not just philosophers), because the past tells us quite a lot about the present and the future.
If we are referring to how these things work for academics, then philosophy and history are distinct areas of study. Being distinct areas of study means that they are generally committed to different methods.
I am not a historian so my knowledge of their methods is not very high, but my sense is that historians (often) operate as social scientists and collect primary and secondary sources to piece together what happened in a historical era at a particular place and time. How did they live? Who did they fight with? What did they believe? What did they eat? What did they do for fun?
Philosophy as the academic discipline exists presently is about argumentation. We argue for claims we believe to be true and we look at the arguments of others. We use logic as our method.
Depending on one's particular area of specialization in philosophy, the history that one needs to study will vary. Many contemporary M&E (metaphysics and epistemology) guys begin with Frege and Russell and know little before then. Conversely, medievalists and modernists will tend to be relatively knowledgeable about their period and the historical events that shaped it (you can't do late modern without grasping the importance of the French Revolution; all Medievalists are familiar with the important events at the University of Paris).
Recent times have made the above distinction a bit more complicated.
Specifically, there are also degree programs now in the "history of ideas." These may cover some of the same topics as philosophers have historically covered. They might be coming into existence in places where "philosophy" is narrowed down to contemporary analytic -- or there may just be a glut of people who want to look at the ideas -- i don't really know.
Even historically, I believe there were some people who did philosophy as history and who studied history as philosophers (though for the latter category, many philosophers were terrible historians!)
tl;dr - lots of overlap in some ways; main difference within academia is research methods (and the narrower scope of the "history" in philosophy).
I see no reason why a philosopher should study history but lots of reason why they would be wise to do so. As you say, it can be a crutch, or even a way of avoiding doing philosophy, but there is also much to be learned.
The main thing to learn is that the history of western philosophical thought leads to a dead-end. This might be the most valuable thing one can learn from studying its history. Then one can abandon the history and start forging ahead.