Re. practical what works in the field...
1. LiPo's are typically more compact and lighter compared to the "same" NiMH/NiCd battery...so they're easier to take a spare with you for even the longest games
2. They're typically more efficient at providing power. It's HIGHLY dependant on your setup/power/wiring...but in general you will see many more shots out of a LiPo vs. a NiMH/NiCd of the same "size". Size refering to the physical dimensions since a "large" LiPo tends to have generous MAh ratings and will go for a long, long, long time.
In short...I suppose you can say "this MAh rating will = this many shots"...but you need to take your personal setup into consideration. And in general...you'll get more shots out of a LiPo than another battery in your gun...not because of the MAh rating itself...but rather because the LiPo that you happen to tuck into the gun will probably have a larger "reserve" of power than a normal battery. Hope that makes sense.