Sure, burning down an animal-testing lab causes severe economic loss to the owner, but, living in a capitalist society, another company simply comes and takes over the business. Therefore, business as usual continues.
Good point.
But I think it can have an effect on that too. It's like a 'deterrant'. So in the same way the criminal 'justics' system's actions are supposed to deter crimes, the ALF actions deter and frighten people off from getting involved in animal abuse (at least at the supply end).
Also, when this happens, it makes things more expensive, which makes the consumer of the products pay more, which means less of ti goes on etc...
The actions of the ALF have many effects on people/society/industry and I think it would need to be studied in quite an in-depth way for us to arrive at a conclusion about whether they are effectively bringing about long term changes/an end to animal industries.
That being said, any disabling of animal abuse could be seen as worthwhile in its own right and certainly the rescuing of the individual animals is heroic.