Based on the enemy draft, your team can anticipate the lanes they will go with. This includes an offensive trilane. If the enemy will go for an offensive trilane and the safelane heroes will be at a disadvantage, the heroes can opt to switch to the offlane instead of forcing an easy to lose battle. For example, 3 ranged enemy heroes against a melee carry would be a nightmare for the carry. The carry may switch with the more survivable offlaner, or the entire safe lane supports can join the carry in the offlane and do an offensive trilane as well. Offensive trilanes are useful against carries that require a good amount of farm to come online.
Being aggressive in the lane has its pros and cons. Applying pressure at the get-go will make enemy heroes play safer, giving you more space to farm. This is done by bringing the enemy hero low through Burst Damage or by trading hits. This forces them to chew through their regen items and force them to ferry over additional Healing Salves, wasting their money.
However, this has to be done with good enough vision as unfounded and unnecessary aggression can lead to one getting killed. An aggressive support zoning out an enemy offlane can easily get killed if the offlane hero has disables and if their level is higher than the support’s.