wordpress plugin and themes are, in general, tested more in single installs than in multisite ones, so...
I do not know whether that is true, but we still have the matter of whether and/or how well one cook of whatever classification can multitask. Some, I am sure, can do that where others might not do so well.
I can do manual updates, i.e. check if something goes wrong, only on one blog and then: if it's OK, I do the same thing on all the others...
That is what I do since it is no big deal if my last one (done first) breaks.