Okay......so what would you do if you forgot to check your resin, and all the water in your tank has got a TDS of 0xx. Then what do you do?
If you have the DI after the pump in the van, it's a simple matter of putting new resin in, not so easy with a full tank of water and no DI in the van.
ps. if you use Gardiners NITO fittings, you have zero problems with leaks, quite costly, but worth it!