Stock vs modified
Having a camera modified specifically for infrared photography would give you the most freedom and control over your images. Shooting infrared with all of the IR limitations of a stock camera is like driving a car with only one gear! Here are some advantages that infrared camera conversion offers:
No external filters needed
Since the IR filter is inside the camera there is no need for having infrared filters in front of the lens.
No filter adapters for P&S cameras needed
Since the infrared filter is internal you no longer need to rig any special filter adapters to your P&S camera to be able to attach IR filters. This is great because those adapters definitely make the camera bulkier.
See through DSLR viewfinder normally
As you already know infrared filters block visible light and having one in front of your lens would also block your view making it much harder to compose, meter and focus. Having an unrestricted view through your viewfinder I am sure you’d agree is definitely an advantage.
Much brighter P&S camera preview image
As you know stock cameras block most of the IR light from reaching the sensor. Therefore having a infrared filter on the lens reduces the total amount of light reaching the sensor since now no visible light and very little IR light is getting in. This forces the camera to really amplify that little amount of light in order to give you a decent preview, which ends up darker, grainer and with much less detail.
Functional autofocus / exposure metering
DSLR cameras’ focusing and metering sensors only “see” visible light and infrared filters block most or all visible light your camera can’t meter or auto focus with an IR filter on the lens. With no IR filters blocking the sensors’ view they are able to function.
No tripod needed
Since the viewfinder is unobstructed by IR filters there is no need for a tripod to help steady long exposures or aid composing or focusing. That’s one heavy item that can be left in the trunk!
Better ISO speeds
Without a hot mirror over the sensor block most IR light your sensor’s full IR sensitivity is unlocked. This allows you to shoot at much lower ISO speeds which all help in producing clean, crisp, low noise images.