I have just replaced my 11-32 10 speed cassette with a 11-34 to get an extra granny gear.
Playing around with the Sheldon Brown gear calculator and reading the specs on my rear derailleur (Shimano 105 RD-5701 GS), I have calculated that I am out of spec for the RD, and have been so with the 32 granny gear, although everything has worked and shifted just fine.

10 speed bar end shifters
Triple crankset: Deore 48-36-26

Shimano's specs and my set up in brackets:
Max low sprocket = 30T (34T)
Max capacity = 40T (45T) calculated: (48+34)-(26+11)=45

Should I have concerns, or are Shimano's specs conservative?