I noticed it auto configures personal hotspot settings, which is probably a nice way of saying it restricts them unless you buy a plan with that feature. Right now, I get poor network quality but free tethering with my t-mobile SIM. If I install the carrier update, I'll have better network quality but no tethering (unless I pay more).
I'll almost certainly install the update because my network connection to T-mobile's network is terrible to the point of unusable 75% of the time, but wanted others to be aware.