they literally do not speed up anything for me becasue they are so relatively rare out in a world.
we ARE speaking of troves right? and not the strongboxes inside the buildings? becasue in a time it would take me to get to a single trove that someone else didn't pick up already - i can loot several buildings worth of fensable items inside the city. its just faster to loot instanced containers in my experience then hope for all the thieves troves to be out in a wild, present for looting. I literally find at least 4 times as many chests i can lockpick than i do troves. even with map markers so I know where to look for them. I just never found them particularly reliable.
and yes, pickpocketing is not viable until you are almost done, which is why I said that I switch to it much later. I like to switch to it because of farming for specific things so I kill 2 birds with one stone there, but its not necessary either. its just personal preference. and STILL better and faster than troves in my experience.
seriously, thieves guild skill line has perks that are good. acess to troves though? not so much. its marginal.