This mod "unfixes" MC-1133, if you don't know what that is, basically this mod makes entities ignore the block's effect when standing on the edge of that block.
On a dedicated server, when installed client side only, the mod only works for your player, and magma block can still hurt you since it is handled server side.
When installed server side, it works for every entity.
When installed server side only, only the magma block effect will be ignored for player.