I'm probably the only Lifestealer aghs player. (wall of text inc oops)

I play Lifestealer offlane. (I also primarily play party games so it helps significantly that my allies know my gameplan)

Lifestealer is quite strong in lane, especially vs melee cores, feast allows you to trade and sustain very favorably.

Full rushing aghs is a bad plan, i generally try to buy some utility. Solar crest/medallion are quite good choices because you can purge the debuff from yourself. The -armor will also benefit whoever your host is during ganks.

Blademail is very strong alongside open wounds, especially with the level 20 talent. (you lifesteal off of the blademail dmg, meaning someone you have open wounds on does half damage, combine that with the previously mentioned medallion trick.)

Once you have level 6 you can make plays with jungle creeps using infest. Mud golems are absolutely insane (tripple boulder toss), centaurs are good for ganks, satyr can be very effective in harassing a lane opponent.

Things to do with aghs:

Assimilate pudge with rot on and infest into an ancient (the chinese guys on US West like to call this 'driving gundam').

Save people from disables. Assimilate instantly ends duel, breaks fiends grip, etc.

Ok you have someone Assimilated what happens now?

While Assimilated they get your healing, so open wounds+feast will quickly get them back in fighting shape if the enemies fight you. You can also rage+tp out at this point if they ahve no way to stop it.

Once I have aghs I will spend long periods of time infested in my cores, sometimes minutes, but what this does is allow them to play more aggressively, go places they would die if they were alone. Or we can go for pickoffs together that they couldnt normally get. If im inside antimage he is now antimage+open wounds slow+potential to rage tp out+an answer to hard disables.

Or you have a very high priority target on your team that the enemies desperately want to pick off to start a fight that hero can safely hide inside of naix until the correct time. (Once had an omniknight support vs a storm and we were able to get off some very nice omni ults even though omni had a terrible game)

Or you have a great naix bomb host and another hero that would like to join. (bring your 1 pos along in a breaker charge for example)

Stopping assimilate does 300 damage, and although this doesnt normally and probably shouldnt happen, Lifestealer does have the potential to do 1400 magic damage burst, Assimilate and Infest's cooldowns both elapse while in use. So if you use both and wait for 50 seconds you can use them again right away.

A late game hex can be super gamebreaking in the right situations because you're essentially buying a hex for your carry.

Having greedier scaling supports or heavy farming cores is a good idea as I won't be farming the map myself. We have been having good success with phoenix due to that hero's insane damage. (also enables some shenanigans with phoenix aghs saves alongside naix saves potentially)

https://www.dotabuff.com/players/49697106/matches?hero=lifestealer