[S]Summoning demons, a good thing or bad thing?

I did a google search on summoning Yeenoghu, because I just did so in
my current game.

My character is an orc necromancer  He just sac'ed a goblin, not
knowing that this would yield a demon.  When Yeenoghu appeared I
nearly wet my pants.  But it turns out he's peaceful.

I tried to determine with a google search whether this is a good thing
or a bad thing.  I can see it being a good thing in that there will be
one less demon to worry about.  But it can be a bad thing if Yeenoghu
turns ugly and summons other bad guys.  If I don't do anything stupid,
like bumping into him with Stormbringer, will he remain happy?  If I
leave him for a long period will he get upset like other pets do?

Thanks in advance,
Bill Doss

P.S.  Slashem is awesome.  Difficult, but awesome.