The solution is to have a copy of everything on your "puter".........I have 424GB's of IL2 on my system, including the original, and one with an unlocked FMB.
I don't! I have a basic B.A.T. install, with two sets of mod folders, today and tomorrow, that's it (Plus the same setup on another duplicate computer). SAS is the repository for anything else I need. To be fair I do use a lot of disc-space on development and testing.
A BIG thank you to all those 'archivists' who preserve old links and obscure projects and seem to be able to travel back in time when its needed. SAS~Gerax, in particular, is one of the best at this!
Of course, my earlier post here is a little 'tongue in cheek', because I like a passionate debate and life is too short to protect the humourless. However, there are several approaches to how you sim and people follow their interests to varying degrees:
For me, Dawn of Flight is WWI in 412! That means the planes TAXI. Just look at Kevin Hoggard's missions or some of mine (being renewed atm), to see the old crates rattling around the airfields in scenes that come to life! This was the reason for developing Dawn of Flight in the first place and these days there is nothing else that does what it does.
We all love The Golden Age too, with a unique flightline and a natural home for the Spanish Civil War and the early Colonial and Sino-Japanese wars. Move to anything else and you are going to miss these.
World at War has a number of beautiful aircraft, ships and vehicles not seen together in this era on any other sim or version of Il2! I'm working on my Battle of Britain and Desert War campaigns again and WAW gives me almost everything I ever dreamed of. Coming up in BATEP07 are the early Ju88's, YT2s family given the PA_Jeronimo treatment, absolutely unique in Il2, B.A.T. once again.
The Jet Age is another era, not properly covered ANYWHERE else: That is to say, that 413, or any other patch, pack, whatever, does not pull togeter the Jet Age material in the way that B.A.T. does, seamlessly.
You want to fly modern jets off the big angle deck steam catapult super-carriers? You can do it independantly, but it will take a LOT longer to figure it out and install the various diverse packages than it will to install B.A.T. Even then, you write a campaign for jets... - Who can you share it with unless you list the same complex procedure you went through to get the jets working? - B.A.T. solves all that like NOTHING ELSE in Il2. You have the ships, the weapons packs (nearly all of them, some still to be released but it is done), the jets, the helos, its all there.
I recently had a discussion about this with Vampire_Pilot, one of the great campaign makers moving to B.A.T., and we were able to upgrade The Jet Age by adding Ship-Packs 2&3 (Asheshouse brilliant 50+ ship expansion with vpmedia's textures and classfile fixes for 412). In this way Vampire_Pilot can upgrade his campaigns and put them out for everyone to enjoy, because of B.A.T.
In addition to all this remember that B.A.T. is made here at SAS. - Where the latest code is being written, the best new features are being designed and tested. The best Flight Models, new Engine_MOD (aknowledged Il2 ESSENTIAL MOD for anything post-410), Weapons and Avionics, like LGBs and TVGBs and CCIPs are developed here BEFORE you will see them anywhere else! Thanks to the awsome modders of SAS the B.A.T. crew are able to help to test this stuff months ahead of the general curve...
Take my B.A.T. away and I could not exist on the thin gruel that others consider 'complete' simming.

nose to grind stone hut hut
setting up what I will be sending you
Many thanks Jim, going through QMB on with a fine tooth comb and a fully modded B.A.T.
jt189 has resolved a lot of object conflicts and made QMB missions for B.A.T. even more user friendly and stable across all modules. This is also helped by the new Universal Static.ini for B.A.T., which resolves differences between old WWI and modern Jet Age vehicle calls in FMB (and therefore QMB). Because that's another thing that B.A.T. does - With the modules for DoF2, TGA2, WaW2 and JTW2 all running off the same basic Il2 install, you get great economy from a B.A.T. install. - Selector - Era Menu - Launch - All in one place. That was also the point of B.A.T.