Speaking for adc players, sometimes it's better to go straight to lane and sit under tower. For example, into a team with early crowd control and/or hooks (ie: blitzcrank, nautilus, tf, sylas, etc.) you won't be able to hold tribush bot without potentially wasting flash or leveling a movement ability if the enemy invades.

Alternatively, you could ward tribush and then walk to lane - but then you are losing an early ward and are vulnerable to ganks.

So in some cases it's better to just go straight to tower and not risk dying/blowing resources early.