Simple SQL Question

HI Experts

Please look at the attached code, it is an auto-generated code by MS Enterprise Library, Can you explain what is the purpose of the check for @@rowcount value and why if it is 0 , we have any concurrency problem. For me , it seems that the TRY/CATCH is enough to handle all errors and if the update have no rows to work on , @@rowcount will be 0 and it is completely OK.
Am I missing something? or I can safely remove this check and stay only with the TRY/CATCH ???

Thanks

ALTER PROCEDURE [dbo].[UpdateVmStatistics]
	@cpu_sys decimal(18,0) = NULL,
	@cpu_user decimal(18,0) = NULL,
	@elapsed_time decimal(18,0) = NULL,
	@rx_dropped_1 decimal(18,0) = NULL,
	@rx_dropped_2 decimal(18,0) = NULL,
	@rx_rate_1 decimal(18,0) = NULL,
	@rx_rate_2 decimal(18,0) = NULL,
	@tx_dropped_1 decimal(18,0) = NULL,
	@tx_dropped_2 decimal(18,0) = NULL,
	@tx_rate_1 decimal(18,0) = NULL,
	@tx_rate_2 decimal(18,0) = NULL,
	@usage_cpu_percent int = NULL,
	@usage_mem_percent int = NULL,
	@usage_network_percent int = NULL,
	@vm_guid uniqueidentifier,
	@vm_if_id_1 int = NULL,
	@vm_if_id_2 int = NULL,
	@vm_if_name_1 nvarchar(40) = NULL,
	@vm_if_name_2 nvarchar(40) = NULL,
	@vm_line_rate_1 int = NULL,
	@vm_line_rate_2 int = NULL
AS
BEGIN
	SET NOCOUNT ON
 
	BEGIN TRY
	UPDATE [dbo].[vm_statistics] 
	SET [cpu_sys] = @cpu_sys, [cpu_user] = @cpu_user, [elapsed_time] = @elapsed_time, [rx_dropped_1] = @rx_dropped_1, [rx_dropped_2] = @rx_dropped_2, [rx_rate_1] = @rx_rate_1, [rx_rate_2] = @rx_rate_2, [tx_dropped_1] = @tx_dropped_1, [tx_dropped_2] = @tx_dropped_2, [tx_rate_1] = @tx_rate_1, [tx_rate_2] = @tx_rate_2, [usage_cpu_percent] = @usage_cpu_percent, [usage_mem_percent] = @usage_mem_percent, [usage_network_percent] = @usage_network_percent, [vm_if_id_1] = @vm_if_id_1, [vm_if_id_2] = @vm_if_id_2, [vm_if_name_1] = @vm_if_name_1, [vm_if_name_2] = @vm_if_name_2, [vm_line_rate_1] = @vm_line_rate_1, [vm_line_rate_2] = @vm_line_rate_2
	WHERE [vm_guid]=@vm_guid
        /* Can you explain this ??? */
	IF @@ROWCOUNT = 0
	BEGIN
		RAISERROR('Concurrent update error. Updated aborted.', 16, 2)
	END
    END TRY
 
    BEGIN CATCH
		EXEC RethrowError;
	END CATCH	
 
	SET NOCOUNT OFF
END

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