Why don't I just kill it with a biocide or bleach?

Many products exist that claim to rid your home or office of mold.  What these products are not telling you is that a dead mold spore is just as toxic or allergenic as a live mould spore.  The only difference is that it does not have the ability to grow any more.  You still have a mold problem!  Mould needs to be cleaned-up and removed from the indoor environment.

In many cases just as pesticides, the biocides used (including bleach) can cause a whole other problem of indoor environmental toxicity and pollution that is just as problematic as the organism it is intended to kill.

If I find mold why don't I just remove it and not bother testing it?

In some cases that is sufficient.  However, you don't necessarily need to see mould growth in order to have a significant mould problem.  Some moulds grow inside the wall cavity without any evidence at all on the visible portion of the wall.  

In many instances mould may be visible in one room of a building, but the source of the growth is in another room or portion of the building which does not show visible evidence of growth in readily accessible areas.

Some of our investigations have resulted in significant mould growth findings where no mould growth was even suspected.

I found mold and have reduced the relative humidity to 30% to dry it out.

Although high relative humidity can cause mould growth, reducing the relative humidity to very low levels like 30% to dry out the mould is not advisable either.  Drying out the mould can increase the chance of it aerosolizing.  Mold has a natural defense mechanism where if disturbed, attacked or is dying, it will send out potentially millions of spores into the air that will settle and grow elsewhere.  Avoid high relative humidity, but also avoid drying out.  A relative humidity of 40% to 50% would be more advisable and have the mould tested and removed.

I found mold growing in a corner of my bedroom.  Should I just replace the drywall?

If you have mold growth you need to know why and how much.  The source of the mold should be identified in order to avoid the problem repeating itself.  If there is a roof leak or other moisture problem it needs to be fixed.

A mould test should be performed to determine how bad the mould problem is, what type of mould it is and if it's in any other portion of the building.  With this data a proper method of removal can proceed.  In some cases a carpenter can replace the drywall.  In other cases the unaffected portions of the building, the occupants, and the people doing the mould remediation need to be properly protected.

We just bought a house and will be renovating.  How can a mold test help?

Especially in scenarios where you don't really know the history of the building, it is advisable to test for possible mold amplification before removing walls, carpeting, or doing another structural work.  If you start removing drywall and see the back side of it black with mould it is in many cases too late.  

Sick Building Syndrome or Building Related Illnesses are increasingly the result of either careless building maintenance, careless renovating practices, or toxic mould exposure caused by aerosolized mould spores due to the removal of building materials without proper mechanical safe guards.