1

In the end it all depends on your route, there's no clear-cut answer to your question. You need to draft an itinerary, look up the price of the rail pass (plus any supplements for high-speed trains, sleeper trains etc) and compare it to the other options for each leg of your trip.

One word of advice for Europe: there are many rail websites with the word "Euro" or "Europe" in their name - ignore these. Every country has its own railway company and while many of these companies accept Interrail or Eurail passes, each have their own fare system and rules. There is no such thing as European Railways, although the marketing people at Eurail (often abusively called "Eurorail" by novice travellers) seem to be doing a good job at making non-Europeans believe there is.
Also note that you're only eligible for Interrail if you've lived at least 6 months in Europe, otherwise your only option is Eurail, which is more expensive and restricted.
See the excellent http://www.seat61.com for everything you need to know about rail travel in Europe and beyond; it also includes a useful discussion about the pros and cons of rail passes.

would it make sense in buying a rail pass for Japan?
That's the only country I know of where a rail pass almost always pays off when you travel its standard tourist l(say Tokyo-Kyoto-Hiroshima-Tokyo). The pass can't be used on the very fastest type of high-speed train (Nozomi) but can be used on every other train, including the only marginally slower Hikari and Kodama high-speed trains; there's a surcharge for sleeper trains, but on the other hands reservations are free of charge.
But again, it doesn't make sense to buy a rail pass if you only travel one-way from Tokyo to Kyoto and don't mind going by overnight bus. You need to do the maths yourself.

2

P.S. note that the Japan Rail pass can only be bought outside Japan.

3

Thank you Aribo! I was just wondering as my itinerary is not yet set in stone but I was interested in overlanding and it seemed like everyone recommended doing it by yourself.

4

Even if you buy the Japan Rail Pass,you are still 'doing it yourself'.

I think you are confusing two completely different things here.

One is doing tours,where you are in a group and you do everything at the same time and together.Very few people on here would recommend that,for a variety of reasons.

The other is a travel pass that might save you money..as opposed to buying individual tickets.You don't travel in a group.
This can be good value...depends on the price of the pass,the price of individual tuckets and where exactly you want to go.

5

As Aribo says,the JR Pass is a very good deal..as train travel is expensive in Japan and the price of the pass is not high.

Eurail is nowhere near such a good deal,but if you are making a lot of trips in a short period,over a long distance,it can be a money-saver.

6

Thank you lucapal as well.

7

An overland pass can be convenient. Take the Baz-bus in S. Africa for example. It takes you from hostel door to hostel door and you can meet fellow travellers en route. It also travels on routes which would be more of a hassle using a public bus (say going from Durban to Swaziland). That said, it is more expensive and there are numerous good buses that can take you to main areas in S. Africa and you really don't need to rely on Baz bus to get around (as some seem to think). I believe the same goes for similar services in places like Aus or NZ.
Bamba bus, if I'm not mistaken, is slightly different in that they use public buses so the only benefit is?? uhm? well, not sure really, maybe ease of buying tickets? It's not that hard though.

8

Likewise for the Fez bus in Turkey. Turkey has an amazing bus network, with cheap and frequent buses all over the country; with the Fez bus you're limited to certain days and routes.
Also, trains in Turkey are slower than buses, and some routes are heavily disrupted at present as they bring the system and tracks up to date. (After 2015 they should be marvellous, but not right now.)