Is there any real benifit to understanding decompression theory?
Eg tissue groups, M values, different algorithms etc

Or is simply knowing you need to follow the tables/computer is enough?

I think you at least need to understand enough to be able to choose a suitable table/computer for the dive you are planning.

I guess the more you understand about the theory the more flexible you can be with adjusting your plan on the fly.
It will enable you to make informed decisions in sticky situations, for instance if your computer wanted to keep you in the water for another 5 minutes at 3m but you were becoming very cold, you could better decide what to do, either blow your stop or risk hyperthermia.

I guess it depends.
If nothing goes wrong, then it's probably fine not to know a thing about it. Then again, it's certainly worth knowing which 'parts' of a profile are considered mandatory, and which parts are just additional safety (eg: on a what's commonly referred to as a 'non deco dive', ascent rate is pretty mandatory, but the 3 minute 'safety stop' could (in theory) be omitted without ill effect.

If I had to get out of the water in a hurry after a deco dive, because of say major equipment failure or environmental danger, if I had the option, I'd certainly aim to get the faster tissues cleared before getting out of the water (and then either head quickly back under water, or to the nearest chamber).

knowledge is power.

Really good book on the subject is

http://www.amazon.co.uk/Deco-Divers-Dec ... 1905492073

Should be able to get it at places other than Amazon.

Actually written in language that people can understand.

I think it depends on what type of diving you are doing, or want to do. If you are allways diving with in no-deco limits, then I don't think there is any real benifit.

If you intend to dive deeper, especially with a bit of Helium added in, then I think it is a good idea to have an interest. There is alot of talk about stuff on the internet, and while some of it is very informative, other times people will state a conclusion they have come to (or are reproducing) as fact.. and it can be difficult to asses the merits of it, or how it applys to you.

Deep stops are a good exaple of this. There's quite a bit of controversy and opinion arround about them. If you actually read up and understand what problem they are aimed at preventing and how they are preventing them, then you can make much better informed decisions arround if/when you use them in the dive(s) you are planning.

On the other hand, you see someone saying... "Deep Stops are great and everyone should do them" and the next thing you know, recreational divers are using them during ascents from deep dives.

Lets take an example of using the PADI tables to plan a dive to 40m (not sure who does now) for no-deco diving, From memory you have 7 mins at 40m. The table asumes/requires a steady ascent rate. If you leave the bottom at 7min and if you stop multiple times at depth coming up from 40M, you could actually be putting yourself at a greater risk of DCS.

So.... I think that if you are going to be using different techniques it is usefull to understand the theory behind them, espicially if you are mixing different theorys (like PADI tables and Deep Stops).
If you never intend to push or come close to the limits of you algorithm/computer, then there may not be any real benifit to knowing the backgroud.