Most crossbow companies sell “arrow speed” to sell Crossbows based on say, a 400 grain arrow/bolt.

Yes, sure, that 400 fps equates to delivered kinetic energy to game but what about penetration?

Will a 500 or 600 grain arrow get more momentum thus deeper penetration. On a target butt, you won’t see a dramatic difference because it is the target butts job to stop the arrow. It is not flesh.

The same crossbow will lose some speed with the heavier arrows but gain in penetration.

African bowhunters on really big game use say 800 to 900 grain arrows. Bolts are shorter but a 500 to 600 grain bolt will carry more momentum thus penetration. 

An exit wound for an arrow provides the all important blood trail.

If hunting moose or larger, for example; With crossbow, use a heavier arrow.

Below is what Fred Bear said on the subject; https://www.arkansashunting.net/threads/what-did-fred-bear-say-about-heavy-arrows.95210/

Good Hunting!