A B-Team is really worthwhile if you play on classic (or insane) ironman where squadwipes can occur. Going against cyberdiscs, elite-mutons and such stuff with rookies is very hard. That’s where SHIV's come in handy in my opinion. They aren't as good as a major or colonel but really help out the rookies so they can get some experience. If you got your squad wiped and have no good replacements send a SHIV with each rookie. I use two alloy SHIVs in front for the rookies to use as cover and one hoover in the back, filling the role of an overwatch sniper.