If your team can see when Blue/Red/Dragon/Baron die, they should have the buff timer given to them by the game. It isn't skillful to add 5/6/7 minutes onto when something died and post it in teamchat. It's just tedious, like denying was in DotA.
Wards are a separate matter that obviously shouldn't be announced, and the game basically already does this if you clear a place on your minimap by giving your team vision of it(if they clear blue, and you go there, you see on the minimap when it respawns.)
Just saying, the game would be a lot more fun for me if it gave you like, a 30 second warning on timers your team has earned. It is not skillful to add 5/6/7 to a random number.
tl;dr: if your team earns a timer by having vision of any objective when it dies, it should be announced. Inhibitors, buffs, etc - anything your team has the right to know about through map presence should be announced by the client, not players who are willing to do the tedious work.
In my opinion, anyway.
Inb4 strawmen about skill of counting