LDAP is nice, as is NIS - if it works and you don't have to look at how the sausage is made.
If you have to built a network that uses any of those, make sure to have plenty of alcoholic beverages for after hours until it works as intended on _every_ edge case.
I've ran a relatively basic installation of NIS for logins on client systems and NFS for remote home directories.
As long as all servers and services were up and running, it was nicely working - but restart one of the servers or services, and all hell breaks loose (especially on the client end) as everything depends on each other (I didn't get the ressources to build any redundancy...). Mix in an old megaraid controller on the NFS host that thinks it's a teapot randomly for ~30 seconds every few hours and you just want to burn everything down.
AD is a completely different can of worms, as it drags in TONS of mandatory dependencies (as usual in the microsoft world...).
NIS can run completely on its own and e.g. just add to the local user/group files. So you can run it for really small tasks on a small scale without major impact or the need to change everything throughout your whole network.
Same goes for LDAP, although wrapping your head around its arcane architecture might be a challenge...
en.wikipedia.org
